To continue this thread:
Imagine trying to maintain battery longevity of a boat at anchor with no one aboard and dealing with the irregularities of sunshine on PVs and/or a wind generator to top off the batteries.
Is it possible or advisable to use a 'sacrifice' battery in conjunction with a voltage booster to continue to maintain the topping off charge on the main group of batteries and another small task like bilge pumps? The 'sacrifice' battery would of course go through many more charge cycles while effectively maintaining the longevity of the battery mains.
- Steve
The Question:
"For battery LONGEVITY, is it preferable to have the battery absorb every
last bit of energy and sit there fully charged with an external float
charger (set to, e.g., 13.2v at 70degF), or is simply turning off everything
when float current gets below a certain point preferable?"
> From: James Graham <osirissail@yahoo.com >> re-charge the battery that is a cycle...
>
> Battery life is measured in "cycles" not hours, days or years. Each time the
> battery is allowed to discharge and then a battery charger kicks in toThank you for emphasizing that the measure of longevity is "number of
> - - Constantly "on" charge battery charges not only keep the battery topped
> off but they will provide the electricity to run the other equipment
cycles", even if those cycles are extremely shallow DOD and last only a few
seconds. I should have pointed out that my series strings (156v EV, 48v
boat) are strictly separate motor-energy suppliers, isolated from the
vehicle/boat's normal 12v system.
> From: Mike <biankablog@verizon.net >
> There are no bad or old questions here just new opportunities to learn
> something. New people are joining the list with new ideas and expertise all
> the time. Your question is something I have been wondering about too. I've
> charged my 48 volt 200 amp AGM battery bank up to full charge and then
> shutdown the charger because my boatyard will not allow any AC lines going to
> boats over the winter. So I am relying on the wind generator and solar panel
> to keep things charged up until I next check on the boat and plug in the AC
> charger. I have been wondering if this is the best way to store and charge my
> AGM's over the winter too. So far the batteries have been holding up using
> this system but, I'm not sure if it is the best way to store the AGM batteries
> over the winter. Since I'd rather not think about taking them off the boat
> every year.
Thank you for your kind words. My normal onboard 12v system stays fully
charged, with the solar panels more than making up for any daily partial
discharges (e.g., fridge), although I'm now a little concerned as after six
years on the batteries the number of "cycles" must be in the thousands...
time to do a precise load test.
Anyway, my conclusion from the discussions is that it is preferable to keep
the batteries sitting on chargers at a true float voltage level and to let
them gradually top up fully each time. I'll be monitoring the current out of
each charger to ensure each battery's float current eventually settles down
in the low milliamp range, as a higher current may be a problem indicator.
Thank you for your help, and wish everyone a Happy New Year!
JoeS.
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