Battery Problem

[Heron]

Hello All,

We recently purchased two new Deka 8D AGM batteries for our dedicated house bank. The old batteries were of the same size and type. The batteries were installed in October of 2011 and we have been cruising on the boat (Monk trawler) since then.

We are having problems with keeping the voltage in a good range. If we run the boat during the day, our batteries are at 100% full according to the LINK 10 monitoring system. The voltage, once the engine shuts down is 12.7 but decreasing to 12.65 within a couple minutes. Over the course of the next 12 hours or less, we consume about 60 to 80 amp hours in our 500 amp bank. The biggest consumer of course is the fridge which uses about 5.5 amps and runs on average 25 minutes on and 10 minutes off. Our LINK keeps good track of consumed amps and gives the percentage of battery amps left and it seems to run consistent with the hours used, usually showing 80 to 88%. The voltage, however, is at 12.05 to 12.1 at that point.

When on anchor, we use the generator to push amps back into the batteries. We have a Magnum 3000 inverter/charger and it is set up for AGM batteries. It can get the bank up to 100% in about an hour to 75 minutes. Again, the LINK 10 shows batteries up to 100% and even while the charger is on, we are gaining 14.5 Volts into the battery charging system. As soon as the generator is turned off, we are back to 12.6 V which is confirmed by the LINK, the control box for the Magnum and again by volt meter directly on the batteries. Over the next 10 to 12 hours, the same scenario occurs, amps down about 65 to 80 amp hours, voltage at 12.05. If we allow the batteries to go 24 hours, we are down 130 to 160 amp hours and voltage is now at 11.80!!!

Am I having a problem with these two new batteries or is this normal. The batteries were tested by another boater when the batteries were at full charge and they tested OK.

Thanks for your help.

[rebel heart]

The 12.6 you're seeing doesn't seem that bad, especially since that's probably under load.

But this math seems a little funky:
- 500 AH bank
- subtract 160 amp hours
- arrive at 11.8 volts

I use regular wet batteries (t105's) but it seems mighty odd that you drop that low when using 30% of your capacity. I don't really know the charging profile of AGM but maybe you're not really topping them off. For wet batteries anyway there's a maddening period that takes a long time to really fill up that top 10-20%.

It wouldn't be hard to arrive at 80% charge, suck out the 160AH, and now you're under 50%. One nice thing about solar (when it's sunny) is that even a modest panel provides that steady high voltage charge current for a long time that batteries love.

Not sure if that was helpful. Sorry bud.

[Heron]

Bud,

thanks for your reply. I also was wondering if my batteries were in fact fully charged. And yes, it does take a lot of energy, especially at the end of the charging cycle, to get them back at 100%. What took that argument away from that theory is when I run the engine for a 8 hour day, I know my huge alternator and smart regulator is without question bringing those batteries to 100%. In 12 hours I have the same problem, anemic voltage in the 12.05 range.

[btrayfors]

Coupla thoughts:

1. Battery monitors like the Link may be quite misleading in telling you the percentage state-of-charge (SOC) of the batteries, particularly with new batteries which have not been broken in and which have not reached a truly full charge before recalibrating the monitor.

2. You could have a weak battery. One way to test this would be to remove all loads from the batteries (including the frig) overnite, isolate the batteries (by removing one of the jumpers), and measure the voltage of each one independently. They should be roughly the same. If not, then there's a problem with the one having lower voltage, particularly if it's much lower.

3. It's unlikely that you could go from 80% SOC to 100% full charge in only an hour or 90 minutes, no matter the size of the charging source. Even with AGMs it takes quite a while to reach a true full charge. You might try leaving the boat on a dock overnight with the shorecharger on, preferably with the load disconnected. Then, next day, recalibrate the Link monitor since, presumably, you'll now have a full charge in the batteries.

4. If you're still seeing a drop from 12.7 to 12.05 within 24 hours, then it would appear that either there is a real problem with the batteries or you've got more load on them then you think. A clamp-on ammeter on the cables near the battery bank would be a good way to find out what the true load is.

Bill

[Bash]

Sounds like a situation where a half-dead battery is drawing down the new batteries. I would suspect that the thruster battery is charging itself from the new AGMs, and actively drawing them down.

Easy to test. Disconnect the suspect battery and see how the new bank holds its charge.

[Heron]

Bash,

That is a good suggestion. There is no battery that is dedicated to the thruster. It has dedicated wires running from the thruster to the house batteries. The engine battery is dedicated to the engine only which is the same issue for the generator having its own battery and depends on the generator's alternator to keep it at full charge.

Don

[Bash]

Originally Posted by Heron

Bash,

That is a good suggestion. There is no battery that is dedicated to the thruster. It has dedicated wires running from the thruster to the house batteries. The engine battery is dedicated to the engine only which is the same issue for the generator having its own battery and depends on the generator's alternator to keep it at full charge.

Don

I understand. You may want to simplify your setup in the future. Not only is it inadvisable to mix battery types, but it's also a bad idea to mix old batteries with new.

[Cheechako]

Try disconnecting each battery from the system one at a time and measure it's voltage after charging. Then measure again in 12 hours and see if it's holding. I've had two near new batteries fail in my boating lifetime. (internal short) Maybe first, feel each battery after a long charge.. if one of them is quite hot... that battery is suspect.
I'm not sure what you are seeing is not typical though. As I remember, my batteries would be a 12.7-13 volts after charging, and by next day 18-24 hours later be at 12 volts or lower even... due to the refrigerator...

[Bash]

Apologies for my prior confusion. I just realized that we have two battery threads going at once, and I was also contemplating the one started by Sulaire.

Please forget whatever I said about needing to simplify the system. But the concern about and older battery drawing down new batteries may still apply?

[donradcliffe]

If you have a clamp-on ammeter, check the current flow out of each individual battery when under load. If you find that one battery is providing 2/3 of the energy, the other one may be weak. Another way to determine the same thing is to disconnect one of the batteries and plot voltage versus time for 6 hours, then do the same thing to the other battery.

You didn't mention what voltage your big alternator charges the batteries at (both absorption and float, measured at the batteries). According to Deka, it should charge at 14.4 to 14.6v at 68 degrees. There's a lot of useful info at

http://www.dekabatteries.com/assets/base/0139.pdf

[Heron]

Hi Don,

Thanks for your contribution to my battery issue. My Magnum charger does show the voltage to be in the range you expressed. I guess I'm just confused why I'm only asking for an average of 75 amp hours in 12 hours out of these two 8D batteries but only have 12.1 volts available at the end of those 12 hours of use. Perhaps this IS normal but in my previous vessel, I would use about 80 amps in 24 hours with 4 T-105 batteries as my bank. When I would look at my voltage, I generally still had about 12.3 Volts still in the battery.

Don

[matauwhi]

G'day, Heron. Based on my experience, when you are on anchor, you are NOT running your generator long enough to fully charge your batteries, even though your Link may be indicating that they are 100% charged.

Next time you run the generator, at the timeframe you would normally shut it off, note how many amps on the Link are going into your batteries. My gut tells me it's well above 10, might even be above 20 or so.

Try running the generator for another hour, maybe even 3, if you haven't motored for a long period of time in awhile to get your batteries back to 100% charged (again the LINK might not be set-up quite properly giving you a false reading of being fully charged). Cheers

[Heron]

Matauwhi,

Thanks for that bit of advice. Yes, I concur with your suggestion of looking at how many amps are going into the bank. Usually, when the LINK is showing about 99% full, there are still over 10 to 15 amps showing positive into the batteries. So I believe you are correct in telling me that the LINK is saying 100% when there is still some charge to go.

I wish when my main engine has been running on a day of cruising of 8 or more hours, that my voltage drops would be less that what I'm experiencing using the generator at anchor, but it seems that after 10 to 12 hours later (after a full day of running) the voltage drops to around the 12.1 Volt area.

One other point. I have measured the consumption of each electrical object on board and confirmed that my LINK 10 has picked up all the electricity being used. I know the fridge uses 5.5 amps, my laptop is 2.1 amps, my lights use 1.2 amps, when inverting, my inverter uses 2.2 amps, etc. When I in fact turn all those appliances on, my LINK10 does identify each additional draw as each one is turned on.

[matauwhi]

G'day, Heron. Based on your numbers, you are using roughly 125 to 150 amp hours a day. You are going easily going to have to run your genset 2 to 2.5 yours a day to keep them charged up while you are on anchor. Your will be just starting to get them near 100% when the amps going into your batteries drops below 5 amps on the Link when charging. All the best. Cheers.

[rebel heart]

Grab some solar panels man, they make a huge dent!