Batteries Discharging While Stored

Batteries, Generators, Solar, Wind and Electronics

Batteries Discharging While Stored

Postby GeoffSchultz » Thu Jan 07, 2010 7:13 am

Yesterday I went down to the boat to see how she was doing. I'm happy to report that all was well, at least until I checked the batteries. I found them at 12.2V and I had left them at around 12.7 V. When I store the boat I remove the + cables the the batteries so they're disconnected from everything. As a result I was quite surprised to see them at this voltage, considering that it's only been 2 months since I did this. However, I did notice that I had left the voltage sense wires connected, which connect to the inverter/charger and solar/wine controllers. I had assumed that these were purely passive and that no current could be drawn from them. However, it would appear that my assumption was false as I have no other answer as to how they dropped 0.5V in a little over 2 months. This is something that you should consider when winterizing your boat. Note that this is the first year that I've had the voltage sense wires.

-- Geoff
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Re: Batteries Discharging While Stored

Postby Ereiss » Thu Jan 07, 2010 8:14 am

Geoff;

What type of batteries are you referring to? Conventional lead/acid, gel?

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Re: Batteries Discharging While Stored

Postby GeoffSchultz » Thu Jan 07, 2010 10:07 am

What type of batteries are you referring to?
8D AGMs - New in 2009
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Re: Batteries Discharging While Stored

Postby Castaway » Thu Jan 07, 2010 7:55 pm

Lead acid batteries always self-discharge even if completely disconnected, due to internal leakage currents. Usually, the lower the temperature, the lower the discharge rate, being minimal at around 0 degrees Centigrade. Leaving them on trickle charge is the best way of avoiding this, but it does need a fancy charger and continuous mains electricity supply. The voltage monitor will draw a slight current, which will accelerate the drain; the only way to find out how much will be to repeat the experiment with it disconnected. If my batteries still have this much charge after a winter without charging, then I shall be well pleased!

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Re: Batteries Discharging While Stored

Postby GeoffSchultz » Thu Jan 07, 2010 9:49 pm

AGM's have a discharge rate of 1-3% per month. Mine went from 12.7 to 12.2 in 2+ months, which is 4% per month. I suspect that there's more at work here than self discharge.

As far as a trickle charge goes, that sounds great. However, my yard doesn't allow boats to be plugged in while in storage.

-- Geoff
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Re: Batteries Discharging While Stored

Postby THATBOATGUY » Fri Jan 08, 2010 5:10 am

Solar trickle.

Just dropping the temperature in the last couple months could result in a lower voltage reading at the battery. Batteries just don't work as well when they get cold. In central Illinois we even had little heater pads to put under them so the car would start on those really cold mornings.

I had a shop teacher who took us out into the parking lot to demonstrate something. We took a volt meter and attached the negative to the negative terminal and then took the positive probe and drug it across the top of the battery from the positive probe to the negative probe reading slight voltage the whole way. Granted it was warm out and these were "standard" lead acid batteries but "keep it clean" is still very important for us boaters. Try slightly dampening the area (as though from condensation) and give your volt meter a work out. I clean our batteries with baking soda and water solution. I'm certain your AGMs are less susceptible to this problem but with salt air and everything...

Also I think that "self discharge" figure of 3% and you with 4% plus the temperature drop could account for your loss. But, I'd still disconnect the sensors just to be on the safe side.

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Re: Batteries Discharging While Stored

Postby SailRI » Fri Mar 21, 2014 3:54 pm

Small solar panel keeps them up fine in the winter, no need to remove from the boat.
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