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post #1 of 8 Old 10-17-2016 Thread Starter
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Serious battery discharge

Hello. I have 2 Trojan T105 batteries that are 3 months old connected in series on my boat for 12 volts. I inadvertently left my inverter turned on, without anything plugged in, and it sucked my batteries down to 4volts(!) before I returned back to the boat, after a month. Anyone have any thoughts on what damage may have been done to the batteries? They took a charge, and seem to be holding it, but I'm concerned.
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post #2 of 8 Old 10-18-2016
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Re: Serious battery discharge

Technical term is "stuffed"

But see how u go

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Re: Serious battery discharge

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Originally Posted by souzag View Post
Hello. I have 2 Trojan T105 batteries that are 3 months old connected in series on my boat for 12 volts. I inadvertently left my inverter turned on, without anything plugged in, and it sucked my batteries down to 4volts(!) before I returned back to the boat, after a month. Anyone have any thoughts on what damage may have been done to the batteries? They took a charge, and seem to be holding it, but I'm concerned.
I don't know of an inverter that does not have a voltage cut off in the 11V range, meaning it will turn off at somewhere between 10.5V and 11V, so you may want to also check for other culprits.

You will have certainly lost some capacity but recharge them then equalize and see how they do. At 4V you had taken them well below 0% of capacity and this really causes extreme levels of sulfation..

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Re: Serious battery discharge

The batteries have taken permanent damage, BUT. It is very possible that you can recharge them (do a slow charge, not a fast one) and while you will have used up some of their lives, they may still be perfectly acceptable, i.e. 80-90% of the life may still be there. If you have a battery distributor nearby (where you bought them?) they are used to this type of thing, and you can usually bring the batteries in to them, where they will put them on an overnight or weekend charge and try to reform them for you. And of course, test what real capacity is left.
DIY or let them, but don't give up until you've taken a shot at it.

Then look online for a "Battery Brain" or similar. These are low-voltage cut-off relays, which will disconnect your batteries from all loads in the battery voltage drops to a set point, like 11.5 volts. Some come with a remote fob to reset them, some use a push button to reset them. Some claim to be "marine grade" but I think any of them might be of use.
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Re: Serious battery discharge

Hello. Thank you for the response. I turned my Mastervolt charger on while I was at the boat, and it went thru the 3 cycles. It took a while to get to float-about 6 hours- and stayed there the rest of the day. I shut it off at night and went to bed. The next morning I did a voltage test and it was 1274. I went about my day, running lights(LED), water pump, even cleaned my bilge and ran my bilge pump so I could use as many amps as I could. At the end of the day, my battery read 1269. Still 100% charged as far as I know. I then turned the B/C back on, and very quickly it was on float. I left on all night, shut it down in the morning, did a voltage test and it held a [email protected] all day, without any use. I'm hoping there wasn't much damage, since the batteries are new. I will be looking for a Battery Brain tomorrow. Again, thank you very much!
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Re: Serious battery discharge

Thank you for your advice. I'll be back on the boat in two weeks, and I'll equalize the batteries then. The only other culprit may be the bilge pump, as we've had a decent amount of rain in the PNW, so maybe(?) that used a crazy amount of amps?? I don't know. Nothing else was on, and the pump is wired directly to the house bank...Thanks, again
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Re: Serious battery discharge

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Originally Posted by souzag View Post
Thank you for your advice. I'll be back on the boat in two weeks, and I'll equalize the batteries then. The only other culprit may be the bilge pump, as we've had a decent amount of rain in the PNW, so maybe(?) that used a crazy amount of amps?? I don't know. Nothing else was on, and the pump is wired directly to the house bank...Thanks, again
A bilge pump with a stuck float switch could certainly run the batteries down.

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Re: Serious battery discharge

Lead-acid batteries can tolerate this deep discharge better than any other type.
You have reduced total life expectancy of the batteries, but it is likely that you can charge them (carefully) and get a decent amount of service from them.

I'd recommend that you get a charge regulator designed for solar systems which has a low voltage protection circuit and add a solar panel or two for when the boat will sit unattended for extended periods. That way the system can keep the batteries charged enough for the bilge pump and even with something being forgotten the batteries are protected from excess discharge.

These controllers are available in a wide range of ratings from cheap appx 5 amp (good for maintaining a car battery and powering a couple of lights) to ones that can manage the power of a large house off the electric grid.

A small setup with appx 20 watts of panels and 5 amp regulator is enough for the bilge pump but wouldn't handle the inverter. You could still connect that to the battery bypassing the regulator but would not be protected from forgetting to turn it off.
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