How "fast" you can reliably charge your battery.

[Rick]

This discussion applies to deeply discharged house batteries and not start-only start batteries. A deeply discharged battery is one which is "missing" 10%, or more, of its potential capacity (note that I did not say "rated" because an aged battery will not exhibit a fully charged potential capacity equal to its rated one).

The answer: A charging current equal to the value of the number of Amp-hours missing from the battery will not excessively gas or heat the battery. This is the so-called "Amp-hour Law" which was proposed many years ago in the literature. Now what's interesting about this concept is that a charge curve following this "law" forms what is called the curve of Epsilon, an ever decreasing curve of charge current. What is also interesting is that when using 3-step chargers having an appropriately set absorption voltage and a sufficiently large charge source the resulting curve will almost approximate the Amp-hour law. When precisely following this curve you can safely recharge an 100% discharged battery in 3 1/2 hours with many AGM and GEL cel batteries and closer to 4 hours for flooded batteries. All lead-acid batteries designed to deliver heavy discharge currents (like you need for cruising with a microwave oven, etc) will be capable of folloing this "law".

If you have, for example, a 400 A-hr bank which is discharged 50% then you can safely begin charging at 200A. Immediatly, of course, the current begins to drop to follow the curve. If you have a battery monitor and an adjustable voltage setting for your acceptance charge voltage you can observe the A-hr value missing from the battery and switch to observe the charge current setting the charge voltage until the current equals the missing A-hr value. Guess what? If you do this you might notice that for your system the voltage required to do this initially might be close to 14.7 to 15 Volts for ambient temperatures of about 70 degrees F. If you keep watching you might notice that with some AGM and some GEL batteries you can leave the voltage there and the battery charge acceptance prevents the charge current from greatly exceeding the Amp-hour law. Note that the Amp-hour law does not dictate that the curve should not be exceeded merely that if you want to GUARANTEE no excessive temperature rise or gassing you may follow it.

Obviously 14.7 Volts is higher than the "normal" setting of 14.4 V for 70 deg. F, yet not by much. You WILL notice, however, that a mere 100 milli-volt change can cause huge current changes, which is why a well regulated source is desirable. Why am I telling you this? Because when Ample-Power and Cruising Equipment (They influenced Heart Interface as well) began promulgating the concept of using 3-step charging they picked a first-approximation to this Amp-hour curve which would, in general, be relatively easy to implement yet safe for the batteries. The IMPORTANT result is that capacity lost to a dischargte cycle can be immediately recovered. Charging a deeply discharged battery at voltages always below the recommended acceptance voltages DO NOT result in capacity recovery on a repeated cycle basis and equalization cycles are required to do so. Using higher acceptance voltages resulting in a closer Amp-hour curve CAN recover lost capacity (unless permanent sulphatation has occured).

[GordMay]

Rick:

I understand your advice that “higher than normal” charging voltages are required to complete the re-charging cycle.

I thought that these “higher” voltages were applied during the “Absorption” (& Equalization) Cycle.

Are you suggesting higher voltages in the initial “Bulk” phase ?

And:
The “Amp-Hour Rule” you cite, seems to be at variance with my understanding of some of the advice offered (by William Darden) at:
http://www.batteryfaq.org/

Darden advises:
1a. A good rule-of-thumb is not to use a charger (or charging setting) for batteries that is greater than 25% of the AH capacity* (C/4) or 10% of the RC rating of the battery or batteries being charged (except 33% for AGM).
* Based on the C/20 discharge capacity

1b. The BULK stage is where the charger current is constant and the battery voltage increases, which is normally during the first 80% of the recharge. You can give the battery whatever current it will accept as long as it does not exceed 25% of the 20 hour (expressed "C/20") ampere hour (Ah) or 10% of the RC rating and wet batteries do get over 125̊ F (51.5̊ C) and VRLA batteries do not get over 100̊ F (37.8̊ C).

2. For most Starting Batteries that are discharged less than 10% of their full capacity, an estimate of time is twice the amp hours to be replaced divided by 90% the current output of the charger.

And:
Many Battery manufacturers recommend that current should be limited to between 0.3C - 0.4C (4-Hour)* at the beginning (Bulk phase) of the charge cycle.
A discharged battery will initially draw the maximum current, which decreases at an exponential rate until there are just a few milliamps flowing (is this the curve of Epsilon ?)
‘Optima’ (Spiracell) Batteries claim the ability to be re-charged more quickly, due to the greater surface area of their plates, and thereby lower internal resistance (3 milli-Ohms ?).

Per your example:
The 400a/H rated Battery, discharged to 50% DOD you can safely recharge at 200 Amps
which is 50% of it’s rated a/H capacity (0.5C rate) ...
Are the manufactureers' recommendations "conservative" because they cannot anticipate the user's actual DOD?

[Rick]

Gord:

Although there is a 100 year-old history of the use of lead-acid batteries there is more misinformation related to their proper employment than there are pills for your headaches. Let's understand that "guidelines" and "rules-of-thumb" are useless in many cases without understanding the underlying fundamentals which are often difficult to understand or solve with simple math. Without knowing what are the exceptions to the rule or guideline one does not know when the action is actually a mistake!

The rules of thumb and guidelines which you mention constitute a body of advice which "dances" around the so-called Amp-hour law which stringently and mathmatically defines a safe limit. Can that limit be exceeded? Absolutely, when one is able to KNOW the parameters of the exact battery and its electrochemistry and measure the parameters which form new limits of operation.

Again, the rules of thumb and guidelines constitute limits forming regions of operation often FAR to conservative for applications demanding optimum cycling. Notice that I DID state that the Amp-hour law applies to batteries designed for heavy discharge/charge cycling and if they are NOT then they are no good for modern day cruising. An example of this would be some of the smaler SLA batteries used in those emergency lights mounted inside of buildings. They are, in general, not constructed with internal current strapping sufficiently large to tolerate high C carging/discharging. This fact is often reflected (yet not always) in a higher Ri.

In all of my years working with batteries in various industries only twice have I met the electrochemists who actually designed the bateries for large production. No one else in the battery manufacturing heirarchy have I met who actually knew about or read the publised electrochemistry literature pertaining to all of the parameters which boggle the mind in what might seem to be a simple reversable equation of chemistry. Most flooded-cell lead-acid battery production facilities use "cook-book" directions and off-the-shelf components to assemble the product. In general, the personnell there do not understand the parameters constituting limits of charging and discharging. Most marketing literature has never been reviewed by the electrochemists due to the financial requirement in minimizing warranty claims which WILL be be affected by any advertising statements construed to allow mistreatment by a user.

In the words of one electrochemist: "If I knew that users of a battery had the means of applying the Amp-hour Law with a well regulated source I would design a battery much better for such deep-discharge applications". "Most battery users have pitiful charge sources and, therefore, we must design the batteries to best accommodate poor charging".

The guidelines that your referred to regarding charging limits in either fractional or multiple terms of total capacity, "C" refer to constant current charging and not, in general, to an ever changing curent forming the curve of Epsilon (yes, often the curve is refered to as "exponential" yet the curve of Epsilon is a specific one, not just any exponential).

No, I am not suggesting a higher voltage during bulk charging because, by definition, bulk charging is current limited with an ever increasing voltage until the voltage limits out to the acceptance value (which I DO claim can be higher than 14.4V @ 70 deg. F).

You will discover that by following the Amp-hour law (if possible, because obviously this requires a different control of the charge source) that the interval between required equalization charging will become much longer. Most individuals do not have the equipment for proper equalization, by the way. Proper equalization requires a constant-current source capable of delivering 2 to 7 % of the potential capacity of the battery until the process is terminated at 16 to even 17 Volts for a 12 V battery (depending upon gassing and temperature and sulphation). Who do you know who has the equipment to do this? Most inverter/chargers are voltage limited to about 15.5V (or even less) and a time-out around 1 to 4 hours, and insufficient time for the proper application of the process. This is because the manufacturers are afraid of lawsuits by those individuals who do not monitor the process properly and have some battery spewing sulpheric acid particulates into a living space for a long period of time. What nasty damage or injury could occur!

You might notice that Hawker battery users, like the electric vehicle racing crowd, are often using multiples of C to recharge a discharged battery in less than an hour vastly exceeding the Amp-hour law. In that case they have a battery tolerant of this yet, even then, the life is limited in terms of possible kilo-Watt-hour cycles. Optima batteries are nice for us cruisers because they are designed to tolerate up to 16V applications which means that the widely variant settings of automotive internally regulated alternators do not destroy those batteries whereupon some (not all) other AGM or GEL types might self-destruct over a short time.

Neat stuff, huh?

Regards,
Rick Young

[GordMay]

Yep - "Neat stuff".
more querries later.
Thanx again,
Gord

[CSY Man]

Whoooop...

Way over my head.

Quick question for the experts:

Does the Link 10 battery monitor "steal" any power while monitoring amps used and voltage displayed?

In other words: Does it cost power to have it installed and in use?

(Meh seem to remember something about shunt (measuring Amps) takes a bit of juice...?)

Rumor says that the Link 10 is almost out of production and that a new and improved model is coming on the market soon?

True?

Right now I am managing and monitoring my lead-acid batteries with analog gauges, and have been doing it succesfully for a number of years.

So, uh, would it be worth the time, money and effort to install one of them fancy digital gauges just to see how much I am gaining or loosing in 4 digits instead of 2?

[Rick]

There are many advantages in using a battery monitor such as the Link 10 rather than attempting to discern just what is happening with your battery using only analog Amps and Volts gauges. I"ll outline only a few of the many (which would require a longer paper to do).

Even if you use relatively expensive !% mirrored analog gauges you will be lucky to achieve readings valid within +/- 2% of the full scale values for each instrument. If you use a power inverter to drive a microwave oven you will need an ampmeter having a full scale reading of about 200A, in my opinion. That means that no reading can be guaranteed to be accurate within +/- 2A. In addition, you will not be able to discern drains much less than that. Most such ammeters use a shunt having a voltage burden in your system of about 100 milli-Volts for 100A readings, which begins to become significant. An analog voltmeter with an expanded scale reading may have sufficient resolution for your use yet will not be easy to read 50 milli-volts of change, a minimum requirement in my opinion.

A proper digital battery monitor, such as the Link 10 has a voltage burden of only 10 milli-Volts for a 100A load, which is insignificant. As discussed in this thread if you desire to minimize engine run times in order to recharge your batteries you need to observe the number of Amp-hours missing from the bank, easy to do with this instrument. In addition, you can easily log accurate voltage drops of your bank for various loads and determine degradation over time.

The real burden of the Link 10 might be the power drain over long peroids of time with no charge source. The drain is about 10 milli-Amps in the sleep mode in low ambient light and as high as 90 to 100 milli-Amps in high ambient light (requiring more drive to the LEDs for visibility) when reading 18.8V (not that you are likely to do so without having a charge source in which case you don't care).

One REAL NEAT advantage in using the Link 10 when on the hook is that you can leave it in the sleep mode which still illuminates the LED bargraph indicating state-of-charge. You can instruct a "dummy" to start the engine if the bargraph indicates two yellow lights and turn off the engine when there are 4 green lights...and that's it! All this assumes that you have properly installed and set up the meter.

I was one of the design team members for that instrument (and many others as well) and am most famaliar with the nuances of the circuit design and operating algorithms. None of my team members remain with the company currently producing the product and, therefore, any new product replacing the Link 10 will not likely include many of the planned and anticipated improvemets which we have since "thought-out". The second that a design is frozen for production we know of many improvements to make for the next product. Nontheless, as long as the original design attributes are maintained a user will benefit from its use in many ways as discussed.

Regards,
Rick Young

[CSY Man]

Aye mr. Rick, thanks for the info.

No, I don't have expensive analog gauges, just the regular amm meter, amp meter and volt meter..Ya can see some of them here

http://cruisersforum.com/photopost//...sort=1&thecat=

Nor do I have high draw items such as microwave, inverter or radar...
THe highest load is probably the fridge compressor, about 5 to 6 amps per hour, 8 hours per day.

I DO have a 150 amp alternator, 3 stage charger, battery isolater (All of the above are the Power Line brand)
Also two 75 watts solar panels feeding the 4 Deka Golf Cart house batteries via a 25 amp Flex charger.

So there ya have my 12 volt system in a nut shell.
(Plus of course the sealed lead acid 1000 cca amp Deka start battery)

Happy with the set-up, but been eye-balling them Link 10 battery monitors.

Don't think I need the Link 2000, but found one of e-bay a few months ago for half price, $250.00, bought it for a friend in the Caribe and shipped it down there....Brand new in the box it was.

Have seen the Link 10 for about $120.00, and have been tempted, but understand installation can be a pain.....?

Try not to run my house bank below 75% capacity so as to extend the life, (As per Nigel Calders book)

Being that conservative I have been telling myslef that I don't really NEED a battery monitor, but ya brought up some good points in the above posting.

And for that Mr. Rick, I will buy ya a beer here i Ft. Lauderdale.

(Seems like every sailor or cruiser passes by Ft. Lauderdale sooner or later, so let me know when it is yer turn)

[Rick]

Hi there, by your own description you fit the need for using a battery monitor. I agree that a two bank monitor is not for you (or most cruisers if they design their electrical system properly). The Link 10 is probably your best solution because it has a separate input channel just for measuring (and indicating) your start battery voltage. In addition, if you are able to obtain the optional temperature sensor you can obviate the need for manually setting the house bank ambient temperature. I do not know if Xantrex is still shipping those sensors yet if you look around you might be able to find one.

Using your boat's electrical system without a battery monitor is like driving your car without a fuel gauge....you just don't really know what's going on.

I'm not sure that Nigel Calder recommends a depth-of-discharge of 75%...he's usually very sharp. From an economic perspective the cost that you spend on your battery bank over its life can be expressed in pennies per kilo-Watt-hour-cycle. The minimum cost occurs when discharging to a DOD (depth-of-discharge) of 50% and not 75%.

By-the-way, discharges are expressed in Amps, not Amps per hour. An Amp is one Coulomb per second, therefore, an Amp per hour would degrade into Coulombs only (like the charge on a capacitor). You have to move those charges through a wire to get Coulombs per second=Amps.

Regards,
Rick

[CSY Man]

I'm not sure that Nigel Calder recommends a depth-of-discharge of 75%...he's usually very sharp. From an economic perspective the cost that you spend on your battery bank over its life can be expressed in pennies per kilo-Watt-hour-cycle. The minimum cost occurs when discharging to a DOD (depth-of-discharge) of 50% and not 75%.

Yes, Mr Rick:

Nigel says to never go below 50%, BUT the less ya go down, the better it is for the longetivity he says..So I sort of set my own limit of 75%.

Without having a digital battery monitor, one of course dips down below the self-imposed limit from time to time, that is why I shoot for the 75....Not the 50.

Hope it makes sense?

As far as driving the car without a fuel gauge, yes and no.
Using my analog voltmeter and measuring the voltage without a load on the system, I can estimate fairly close the state of charge:

I.E. 12.4 is 50%, 12.6 is 75, 12.8 is 100%.

And so on...Not on the boat right now and don't have the graph in front of me, but that is about the numbers....?

The optimal battery temp sensor?
Uh, won't the that be ovekill and influenced by the time of the year and the ambient temrpature?

My cruising grounds here in Florida and the Bahamas can go from a low of 40 F in January at night (Inside the vessel) to 100 F in the Bahamas in July. The house bank is under a setee and would surely be affected by the weather/sun as much as by use and charge/discharge.......?

(The above is a question, not a statement, therefore I am listening loud and clear.. )

Based on yer above response, I really need a Link 10 monitor?

Any other products out there that is as good better for my needs?

Again, the expert advice is highly appreiated.

Beer coming up.

[Rick]

Csy man:

I'm very famaliar with curves showing voltage versus level of charge for batteries. Those curves are generated in the lab and are based upon a fixed temperature, a known conditon of the battery after charging or discharging, a known time for making the measurement after letting the battery stabilize, a known beginning specific gravity of all cells, and NO LOAD or source of charge. Change any of these conditons and all bets are off.

Because of the dynamics involved with battery usage in the cruising mode it just isn't practical, or even possible to accurately use voltage to infer the state of charge of your battery in such a real world and, therefore, the numbers that you quoted are wrong except for exceptional cases.

As an additonal thought I like to use the case of automotive start batteries. Even in the days of muscle cars with large engines and starters it would be unusual to use 3/4 of an Amp-hour to start an engine from a stock battery which might ostensibly be rated at a one-time dishcharge of 80 Amp-hours. After six years of daily use, each time the engine fired right up. It did so on Friday. The next day on Saturday the engine ground slowly and would not start. On each day the standing voltage of the battery was effectively the same (for the same temperature: 12.7 Volts. So, on Friday the battery measured 12.7V before starting and on Saturday it still measured 12.7V yet the engine would not start, why? When new the battery could have exhibited a single time discharge measurement of perhaps 80 Amp-hours. Guess what? On the Friday before the fateful failure to start had the battery been measured with discharge it would have crashed after about 1 Amp-hour. Here we have the case of a battery being fully charged yet its 100% state of charge was for a 1 Amp-hour battery. What good does the voltage reading do in such a case? Almost NOTHING.

With a good battery monitor you will be able to observe just when the battery is qualified as being "full". Just what constitutes full? There are many parameters used in the monitor algorithm to determine when the battery is full and one of them is that the engergy removed on a previous cycle must be returned on the subsequent charge cycle else "full" will not be declared. Your voltmeter cannot show this.

BTW, did I mispell optional on a previous message? Sorry!
Cool, huh?
Regards,
Rick Young

[CSY Man]

BTW, did I mispell optional on a previous message? Sorry!

Not sure ya did Mr. Rick.

I tried to go back and look for optional, but in my blurred state of, uh, beer induced discharge, I did not see it.

At any rate...Roger on me being in dire need of a battery monitor.


Been running the present set-up for 4 years now without a problem, and uh, so far it works good.
(Perhaps the 150 watt solar panels keeps me out of trouble?)

Yes, the muscle car example:
Been there: Bought a new car on lease for 3 years...4 weeks before the lease was up, the battery refused to start the SUV...The day before it did start the thing..I kept jumper cables onboard until the lease was up.
No warning kind of scenario..Either, or not..
Correct me if I am wrong, but won't deep-cycle batteries give ya plenty of warning with a slow but sure degradation?
As opposed to a start battery that either starts the engine or don't?

There are many parameters used in the monitor algorithm to determine when the battery is full and one of them is that the engergy removed on a previous cycle must be returned on the subsequent charge cycle else "full" will not be declared. Your voltmeter cannot show this.

Yes, but....:

When I run the engine and I monitor the amp meter pumping juice into the batteries, starting at say 100 amps, then slowly but surely dropping to 0 amps over a period of 90 minuttes, then I know my batteries are fully charged....No doubt?

Uh, Mr. Rick, not arguing yer expertise here, but would it be possible to cruise happily forever after without one of them digital battery monitors....Like in the old days...Just by being conservative with usage and liberal with charging?

In other worlds:
I cook gourmet meals without a microwave.
I navigate safely withou a chart plotter and radar.
I have a nice airflow and temprature in the boat without A/C
Etc...

Surely I would like to install one of them gizzmos, but uh, I am doomed and gloomed without one...?

[Rick]

Yo, CSY man!

Regarding the use of deep-discharge batteries for starting please read the thread on how to determine the minimum reliable size starting battery and why one should NOT use deep-discharge batteries to do so. (BTW: no, deep-discharge batteries will not necessarily give you a slow indication of impending death).

If you are interested I should start a new thread regarding battery charge acceptance and how to use that as one (amongst others) indicator for determinging when a battery is full, sufficiently full for beginning another charge/discharge cycle, and recovered from sulphation or has permanent sulphatation (note different from sulphation).

Now let's make a simple differentiation here (arrrrgh!). Ernest Shackelton most certainly did not NEED a microwave oven or a depth sounder or any other electrical/electronic device to bring his men from Antartica back across the Antartic Ocean in small and almost open boats to survive. Yet barely survive is all that they did. One is doomed and gloomed only without air, water, food, shelter, and perhaps hope with desire. He made the choice to do so in order to survive. WE, on the other hand, are not choosing to cruise in order to survive (except perhaps argueably on an existential level and I have no problem with that philosophically speaking...again arrrrgh!). If Shackelton had Larry Pardey's boat he would have been in relative heaven by comparison. I have been on that boat and listened as Larry expounded on the down-to-earth basics of minimilist cruising doing without the latest in electronic (and other) technology. Nonetheless I could not help but notice the incursion of a CD player and a special neat wooden storage area for the CDs and player and, yes, even he had to have a battery and reading light (and, GOSH, some means of charging the battery!) It appears that the technical nihilist has succumbed to at least one of the desires of the flesh to enjoy life beyond the basics!

By observing the uploaded photo of your navstation it is obvious that you seem to enjoy a few of the niceties offered by technology as well. Do I spy an SSB there which you certainly do not NEED? Could you not get by without one? Does having that tool perhaps reduce your anxiety at being incommunicato? It certainly does so for me. I remember when I first installed my SATNAV with speed and heading sensors. My anxiety level dropped greatly when I was navagating around all of those islands in the Carribean having a greater precision than what I had using sun, moon and star shots, when and if they were visible. My ded reconning was vastly improved. Next I got radar and, again, my anxiety level dropped. My engoyment increased in spending time sailing around (or motoring into difficult areas not easily sailed).

No, you do not NEED any of the stuff that I have been writing about. If, however, you would like to have more security and understanding in/of your boat's electrical sysem you might WANT to have a battery monitor and learn just how to interpret the measurements and checks of which it is capable.

You, like most cruisers having batteries, have learned just what works for you and how to get by with what you have. As you pointed out in the case of your SUV failig to start, wouldn't you have preferred to have some checking ability to determine in advance that your battery was aging towards an inability to deliver sufficient starting current under load? A digital voltmeter and ammeter would have helped. I doubt that an analog voltmeter would have shown the real dip in voltage under load that a digital one would have. BTW, do you have a hand-held DVM aboard?

Later,
Rick

[CSY Man]

He-he Mr. Rick:

Let me start a short reply here and continue later as this is indeed
cutting into my beer time.

Well, no, I don't use a deep cycle battery for starting.
(Did I say that?)

Uh, Ernest Shacleton:
Yes, he made it and barely so.
Bet he wished for a GPS and a Perkins diesel.

Not going quite that basic here in the CSY world, around them Bahamian Island, but somewhere one has to say stop..?

Yes, I have 2 SSB radios, one receiver only that came with the boat....A great back-up.
And I added a SEA 235R Transceiver later...Love it.
Also have 2 VHF radios hard-mounted, one of them hooked up to the GPS shown in the picture...Plus an ICOM handheld VHF.
And an old "spare" VHF tucked away in case a lighting strike takes out the operating radios.

Also have 2 primary electric bilge pumps on separate circuits with separate swithces and plumbing, plus the manual Gusher-10, and uh, a 3rd electric one that I use to suck the residual water out, like a scavenge pump.

I also carry 3 dinghy oars on the boat..In case I loose one.

And have lost quite a few oars over the years.

Ah, more later, now back to the beer-table.

(No, not paranoid about back-ups and gear and so on, but having been a pilot for some 27 years, I sort of made this boat like a Boeing 767, back-up for the back-up, etc...Just in the blood)

[CSY Man]

Continuing on.

Well, as far as the battery monitoring system, or the lack of it:

Lets bite into the above statement:

being conservative with usage and liberal with charging?

Would that not reduce, or eliminate the need for the Link 10?

(Yes, I am playing the Devils Advocate here, bear with me.)

A sophisticated, digital battery monitoring system would of course complete the Boeing 767 analogy...On the other hand, I also flew DC-3s for a living some years back.
Those airplanes were designed in 1935, way before the computer age.
Ya know how they tested the strenght of the wings?
The laid the wings on the ground and drove a steam roller back and forth to look for week-spots...
It worked: 70 years later, the DC-3s are still flying strong, very few wing failures have been recorded despite a lot of abuse, war-time and civilian "bush-flying".

Uh, and my point is?
Ya can probably cruise happily forever without the gizzmo we are talking about if ya love yer batteries and don't try to take too much out of 'em.

Hmm, probably rambling here, but uh, I also keep a digital multi-meter on the boat and the old fashoned tube to measure specific gravity of the battery fluid.

Should all else fail and I run both the start and the house bank down so I can't get the engine cranked...Well, there is the solar panels.

If we have a cloudy day, uh, there is also a Honda 600 W generator onboard, and 2 sets of starter cables as well as dedicated 4 stroke fuel..Always fresh, just in case...

[billangiep]

CSY,
I have almost the same set up as you, it has also worked for me for years. I have digital amp. and volt gauges. but I do have to agree with Rick If you want to know exactly whats going on with your batt. then a monitoring system such as the link 10 is the answer. I know when my battery's are charged by looking at the amp. meter when the engine is running. I know when I need to start charging by looking at the volt meter...but have know clue only a guess as to there condition as they age. How many amp. hours taken out versus how many put back in. A new house bank of two golf cart type batt. has an amp. rating of 225 amp. hrs. or there abouts, but as they age say after a year or two those same two batteries may only have a cap. of 150 amp. hrs. but still have a voltage reading of 12.8 the link 10 would tell you this. So for the price I paided for the amp. volt meters about 180.00 bucks I could have saved about 50.00 dollars by buying a link 10.
Hmmmm.

Bill,