One more battery rabbit hole

[avanti]

Originally Posted by markopolo

Batteries are either being charged or they are discharging. It's one or the other. Self discharge is slow but it is still discharge.

Yes. In the long run, entropy increases. But (assuming we are talking about RV winter storage) as a practical matter, I do not believe that there is any reason to do more than (a) fully charge your battery; and (b) disconnect its negative terminal.

[booster]

Originally Posted by markopolo

Batteries are either being charged or they are discharging. It's one or the other. Self discharge is slow but it is still discharge.

Battery Sulfation : Technical Support Desk

Interesting article, especially the incredibly short time to develop sulphate, although they didn't really say if it was the bad hard sulphate or normal sulphate from self discharge. Also they mention not storing without a power source on them. Seems pretty contradictory to the 90 days that Lifeline talks about. I wonder if the sulphate formed from the self discharge in an AGM hardens over time, and if it does, how long does it take? It would seem to indicate a pulse like Marko's charger every day might be a good idea. I may have to consider raising the voltage I program in for recharge on ours so it happens more often.

[markopolo]

I just checked the amps in on mine after reading Booster's post. 0.3A flowing into 300+lbs of lead acid batteries to keep it all at 13.2vdc. That includes the two engine starting batteries. Some current is probably going to the relay that automatically connects the house and engine batteries.

It's just a trickle going in. 96 cells being fed and kept happy in my unconventional setup. It's close to 400ah house + 2 heavy duty starting batteries.

The trickle does add up but some of it must just be lost in the effort to keep them all at 13.2vdc.

Edit: the solar controller display would also be sipping tiny a bit of current. The backlight goes off automatically but it displays info all the time. (van is in garage)

[markopolo]

I like the periodic boost in voltage. I think it is good but it is just a gut feeling, no real data to back it up, just something I observed here.

I have a starting battery that wasn't too old when I pulled it out of the cab of the van and replaced it with an AGM. It sits connected to a Battery Minder all the time. Each year around this time I bring in the lawn tractor battery and put it on the battery minder (13.1v measured when in use). I end up connecting them all together but for a few days until I get around to it the starting battery rests and settles at 12.55 volts. This year is the same as last. If I put that battery on a bulk charger overnight and let it rest a day the voltage will end up at 12.6 something volts.

That tells me that the trickle charger keeps the battery in reasonable condition but not optimal condition.

It might also indicate that batteries need to be used once in a while.

[markopolo]

A couple of observations from today:

1. Last night I put a bulk charger on that spare starting battery that sits on shelf with a Battery Minder connected all of the time. I disconnected the charger this morning and after 9 hours resting the battery reads 12.67v. Hopefully I'll remember to check at 24hrs. It might be worth leaving it off any charger to see how long it takes to get down to 12.55v - that's the resting voltage I see after taking it off the Battery Minder.

2. I happened to notice 14.4v on the LCD in the van this afternoon. I grabbed my clamp on ammeter and measured 1 amp flowing on the cable from the charger to the batteries at 14.4v. I caught it right before the end, maybe at minute 14 of the 15 minute boost to 14.4v cycle. I think that tells me that all of the batteries in the van are fully charged.