Mysterious battery drain... where to begin?

[reed1v]

Sounds like old batteries and colder weather. Never heard of leaving batteries hooked up unattended through a long winter layup. In any event make sure your positive terminal is well covered whether you leave it hooked up or unhooked. Also make sure the battery surface is clean.

[TheThunderbird]

Truth is... all bats are little S#@t, and we pay good money for crap

[Bleemus]

Leaving fully charge batts unattended through winter isnt an issue if there is no load on them. My guess is he has a bad battery.

[StuM]

Originally Posted by Bleemus

Leaving fully charge batts unattended through winter isnt an issue if there is no load on them. My guess is he has a bad battery.

While they are better than FLA, AGM batteries still self-discharge and with an older one, it can be as much as 2% per week. That means that after 2 months, one could be down to 85% - and sulphation rears it's ugly head. Give it another couples of months and you are down to about 70% and the sulphation will be starting to kill them.

[mitiempo]

Originally Posted by StuM

While they are better than FLA, AGM batteries still self-discharge and with an older one, it can be as much as 2% per week. That means that after 2 months, one could be down to 85% - and sulphation rears it's ugly head. Give it another couples of months and you are down to about 70% and the sulphation will be starting to kill them.

If the temperature is warm batteries will slowly self-discharge. But in cold weather batteries will not self-discharge much at all.

[senormechanico]

Originally Posted by Bleemus

Put the battery monitor on a switch? Nobody is looking at it when your off the boat right?

30 ma is nothing.
With my solar (similar to yours) I have nearly an amp and a half 24/7 draw and don't think anything of that. Ultrasonic barnacle basher, always on backlights (my choice) various led displays (also my choice) etc.
Don't forget, I have LiFePo4 cells which are a game changer, and hard to believe until you experience them.


After looking at that battery post, I think you might have a shorted cell.
That is where I'd start the search.

[OrangeCrush]

Thanks for the input, all. I will definitely get that book. Marine electronics is one of the areas I need the most education on. I'm fortunate that my boat was professionally rewired during its recent refit so it doesn't suffer quite as much from the patchwork of fixes found on most older boats. In fact, just working on understanding what is already in place has been a pretty decent education in itself. That is not to say that it can't have a problem or some bad wiring somewhere, of course.

As for that corroded battery post, I realized that is the connection point for a wire leading downwards, presumably to ground the battery bank to the keel. On further inspection it's really not that badly corroded, but I'm not sure if this is a bad sign.

The inverter has a small fan and so does the refrigeration but neither are getting any power with the house bank switched off. I'm guessing that the 20-30mA fluctuating draw is coming from the battery monitor itself since I don't can't find anything else connected to that wire. And the suggestion that smaller sources of "ghost" drain are adding up is also possible, but if that were the case I would see that amperage on the battery monitor or on the multimeter. The 35mA of draw would be consistent with monitor not showing even a -.1 amp draw. The monitor never shows any amps being drawn or any amp hours being used even when the voltage drops over time. The percentage stays at 100 and as I keep charging them up again the monitor shows a huge surplus of total amp hours.

So I agree that it is probably a bad battery or multiple bad batteries. I will report back when I check them again in a week or so.

Do people think it's acceptable to replace part of a battery bank if some still seem to hold their charge, or is it wiser to replace all 4 to avoid damaging the new one(s)?

My boat has two high output alternators and I am adding 200w of solar to keep things topped off at the mooring next year. It seems like I should stick with AGMs. Is it important to get ones that are designed with solar in mind (like the Deka Solar 104aH) or is that just a label?

[Stu Jackson]

Originally Posted by OrangeCrush

It seems like I should stick with AGMs.

Why do you think that?

AGM Battery Issues (from Maine Sail)
AGM Batteries - Making The Choice | SailboatOwners.com Forums

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries | SailboatOwners.com Forums

Additional Observations on the Limits of AGMs Electrical Systems 101

[rognvald]

Wow! This is deja vu all over again. If you have an older Xantrex unit, like mine, you are accumulating negative amp hours on your meter which, in reality, have no real depletion of the battery system. You need to load test and check the voltage of your batteries with a meter(which is what I did) when I was showing -176 amps on a 220 amp battery system. My meter read 12.4 volts and when I put a load tester on the bank it was perfect. I called the tech at Xantrex and they basically "double-talked" me through my issue with no real answer. The older units were defective, in my opinion, and after that experience I use it only for voltage readings AFTER I have deleted the negative amp hours shown on the unit. Whenever I leave the boat, I disconnect the fusible link. Here's what an earlier post noted: "sounds like a Xantrex system. the link 10 will pull a little current, also current feeds the memory chips on AM/FM radios, stereos, A/C units. all these vampire loads add up with the cold and deplete more than what the perfect-condition calculations might have you believing." Good luck and safe sailing.

[mitiempo]

There is a constant small draw from the Echo Charge as well.

Best to replace the entire bank at once. Old batteries in the bank will lead to a short life of the new batteries.

Don't worry about a "solar" battery. Get good deep cycle batteries. 6 volt golf cart batteries are the best cycling value, lasting a lot longer than 12 volt batteries in most cases. Golf cart batteries are available in AGM. Why do you think you should stick with AGM batteries? Best bang for the dollar is flooded batteries though and they will last as long or longer than AGM if treated properly. They will also cost less than half as much. They are less fussy in their charging requirements than AGM batteries.

Battery monitors need more than just looking at. They develop inaccuracies over time. This should help: Keeping Your Battery Monitor More Accurate Photo Gallery by Compass Marine How To at pbase.com

[rwidman]

Originally Posted by ramblinrod

Original post was correct.

If the battery circuit is open (no load) and one disconnects the battery positive terminal and positive post, the voltmeter will read 0 Vdc. There is no potential between the two, because the circuit is open elsewhere.

If the battery circuit is not open (loaded) and one measures a potential between the disconnected positive terminal and battery post, that indicates there is a closed circuit (load on the battery) and the only thing currently disconnecting it, is the gap created by removing the battery terminal.

Yes that would work but most people would use an ammeter because it's current flow that we're looking for.

[Stu Jackson]

Originally Posted by mitiempo

Battery monitors need more than just looking at. They develop inaccuracies over time. This should help: Keeping Your Battery Monitor More Accurate Photo Gallery by Compass Marine How To at pbase.com

In addition, consider this:

For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

Link-series Charging Algorithms -- The "Gotcha" Factor!

DEFAULTS are factory settings that are made to be modified to suit your setup.

Also read this one:

Programming a Battery Monitor (by Maine Sail)

Keeping Your Battery Monitor More Accurate Photo Gallery by Compass Marine How To at pbase.com

[tkeithlu]

There are very expensive battery testers on the market. For the individual, the old fashioned resistance coil tester does a less sophisticated but adequate job ($21.99 at Harbor Freight, but available at any auto parts store). Charge up your batteries, then attach the big alligator clips (like jumper cables) to + and - poles, see the voltage, then apply the resistance coil (switch). The test coil gets hot. A good battery will maintain voltage over ten seconds or so, while a bad one will drop like a rock.

[rwidman]

Originally Posted by carambo46

What Jim said you'll find out within 5 minutes if you have current drain with an amp meter not a voltmeter and most will tell you use the negative battery post to decide amperage flow

The current is the same at either battery terminal. It doesn't matter which one you disconnect to make your measurements.

[mitiempo]

Originally Posted by tkeithlu

There are very expensive battery testers on the market. For the individual, the old fashioned resistance coil tester does a less sophisticated but adequate job ($21.99 at Harbor Freight, but available at any auto parts store). Charge up your batteries, then attach the big alligator clips (like jumper cables) to + and - poles, see the voltage, then apply the resistance coil (switch). The test coil gets hot. A good battery will maintain voltage over ten seconds or so, while a bad one will drop like a rock.

That will tell you absolutely nothing about capacity of a cycling battery. It works well for start batteries only. The only way to get an accurate answer is to do a true capacity test over 20 hours - or more accurately the time to get to 10.5 volts.