Something is chewing up my batteries

[aesandiego]

Hi. I have a 3 batteries (105Ah each) house bank and 2-battery engine/windlass bank, all lead acid, in my sailboat. When I bought the boat, 5 months ago, the house bank went from 12.9v to 12.2v after just 40Ah of use (according to the amp-hour-meter installed, which shows same V & Amps I measure at the batteries). I only have an icebox drawing any significant current while docked. Batteries seem to charge normally (with solar power, Victron controllers). Battery pros load-tested them and said they were still good. After doing more testing and equalization, I couldn't get more Ahs, so I replaced them to go cruising. They would measure 12.6v after 40Ah. Now, 4 months later, the same thing is happening with the new batteries. After 20 Ah of use they measure 12.2 v.
I let batteries rest for an hour, before making measurements with no load. 2 weeks ago I realized I had the engine/windlass batteries connected to the house bank for months, and the windlass battery was bad (didn't hold charge, I have since replaced it). So it's possible that charging the new batteries with the bad one chewed up the new batteries?
Has anyone seen this kind of issue? Help please.

[S/V Illusion]

To state the obvious, interconnecting 'good' with 'bad' batteries adversely effects the good ones by 1. drawing down the good ones and 2. causing the good ones to over-charge as the charger can't differentiate among the interconnected batteries. That's why its important to verify how the wiring is arranged.
Expensive lesson - always verify how batteries are connected.

[Joh.Ghurt]

No clue, what might apply in your case. Here are a few random things I experienced with batteries that didn't keep the charge.

• Check the battery water level. As an advanced check, get for a few Euros a bulb to check the acidity. I've heard from people around here, that in very hot weather and dry the water can evaporate quickly.
• If you can, charge all batteries and then unplug the one losing most power completely (remove + is usually enough) and let them rest for a few weeks. If the unplugged battery keeps the charge but others don't, you have a consumer you aren't aware of. This could be stupid stuff like the solar charger using the battery to keep running.
• If you have consumers, time to start measuring the Amps in the circuit when you believe you have no consumers.

Other than this, I don't have many clues and hope other people with more experience have better suggestions.

[Naughty Cat]

Could be that a piece of equipment is not earthed. Happened to me; no earth on the watermaker and I had to recharge the battery if left more than about three weeks. Thought it was a bad battery, changed the battery (€500) and problem had not gone away. Then a local showed me how to put a voltmeter between the negative on the battery and the earth with everything switched off and I could see a residual draw. Then it was a matter of putting the meter across bits of kit until I found the culprit. I was still too late to save my aluminium rudder stock which was slowly dissolving away with the leak.

You could take this over to the electrical forum.

[aesandiego]

John, Naughty Cat, thanks very much for your helpful thoughts. I'm going to spend the day troubleshooting the electrical system, doing the tests you propose. I will post what I find.

[GordMay]

Originally Posted by S/V Illusion

To state the obvious, interconnecting 'good' with 'bad' batteries adversely effects the good ones by
1. drawing down the good ones ...

Indeed.

[gamayun]

Would love to hear what you do find out and your process. I think I'm having the same issue.

[Zzmeyer]

For about $200 you can get a Victron BMV 712 monitor. Easy to install. You can track energy usage of every single device on your boat. Others make a similar device. I have been able to chart daily energy usage precisely. For example, I was surprised to see how much energy my inverter was using in standby. My big users are fridge and autopilot.

[aesandiego]

I do have a PusTronik battery monitor which gives me Amps, Voltage, and AmpHours used; super useful. It's directly connected to the house battery negative pole and yields same values I measure with my volt/amp-meter. I found a blown fuse in the battery separator circuit (which doesn't seem to work even with a new fuse). The engine and windlass batteries were not being charged, except when I connected both (house & engine) battery banks. The windlass battery was shot, and likely draining the house batteries whenever they were connected. The negative pole of all batteries are correctly connected to a common ground on the engine. All my batteries are now new (ouch!). I'm replacing the battery separator with an ACR battery combiner, and will keep an eye on both battery banks to make sure they're charging/discharging correctly. I'm hoping this will fix the issue.
Getting to know a new boat is always challenging and takes time, in my experience. I appreciate your help.