sla and agm battery charging

jniolon

Member
I]ve been working on getting a mobility scooter working for a while off and on. It had 12v 15ah batteries(2) and both were dead. I put a battery minder on one and it came right up to 13.5 volts and stayed there for a few days... I tried #2 and it would go no higher than 8.4. Little research on the web found a procedure for putting the dead battery in parallel with a good one and hooking a charger to the good one. (this was to fool a smarter charger into thinking it had sufficient charge to work) Well, after a day on the trickle charger both now read 13.6 or so.

Next story.. different scooter... I have two 12v 35ah AGM that are both reading 1.4 v with no charge... I can get them to charge but they quickly drop back down to 1.4/1.5 volts... I tried the same approach as above but with a standard car battery (wet cell) and got no good results.. so I guess it works for sla only. Anyone have a suggestion for trying to recover the 35ah batteries, they are about 80-100 bucks a piece.
 
The first set, "maybe" they will work, but wouldn't put too much faith in them.

How old are they? About 3-5 years is the typical life for them. If you do replace them, replace both, don't mix old with new.

The second set, doesn't sound good. Best quit while you are ahead before something explodes or overheats.

You really need to invest in a good charger to get the most life and safe operation from them.

Where did you price the batteries? Any of the sealed lead acid or AGM's that are of the same or higher ampacity, and will fit in the battery compartment should work. No need to go back to the mfg for them.
 

3 out of 4 batteries have failed.
DO NOT use an old and new battery together .
A dumb charger will go too high on the voltage and gas an AGM battery to an early death .
If somebody has been deep cycling the batteries . That is running them dead prior to charging . Instead of at most discharging to 50% then charging . The batteries will have a short life span .
There are drop in replacement lithium batteries with internal charge protection . They will give more total range ,
charge faster , weigh less and have a longer service life .
 
Thanks Steve and all

checking internet prices and the average is about 85 bucks a pop.
this project might have to wait till stimulus check #2

j
 

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