Lead Acid Battery testing advice?

[@Michael]

I have two 100AH lead acid batteries that came with my one year old 2019 Coachmen Crossfit that I don't think are healthy.

Here's what I know (or think I know):

If I leave the coach plugged in for a long time (a week) the charge current from the WFCO converter & solar panels tapers off and the batteries presumably are 100% charged.

If I then draw a moderate current from the batteries (5-8A) the battery voltage drops down to 12.2V in a few hours and triggers the low voltage disconnect. Presumably I'm getting something less than 20AH capacity from 200AH of battery before hitting the 12.2 volt threshold. That doesn't sound right to me.

It been cold - say about 40F when I tested. I'm assuming that at 40F I should have been able to extract around 40% of the batteries capacity befor hitting 12.2V, but I'm only getting a fraction of that.

The batteries are a no-name 12v deep cycle battery that was presented as 'sealed' but in reality have flush screw-in caps for the cells. Actual brand is "Xpedition 31DCM deep cycle battery".

I dropped them down from under the coach and have them on the bench. Cells are full to within 1/8" or so of the fill marks. Specific gravity at 40F is 1.28-1.3.

I'd like advice on steps to take to determine if the batteries are working as expected or not. I.E. - if at 40F a lead acid battery only is expected to have 10% of it's labeled capacity then the batteries are good and I just need to move a thousand miles south.

If they are junk, I'll probably put new AGM's back underneath the coach and call it good. Getting at them is a PITA - it's not possible to reach the terminals or caps while they are mounted under the coach.

[booster]

Originally Posted by @Michael

I have two 100AH lead acid batteries that came with my one year old 2019 Coachmen Crossfit that I don't think are healthy.

Here's what I know (or think I know):

If I leave the coach plugged in for a long time (a week) the charge current from the WFCO converter & solar panels tapers off and the batteries presumably are 100% charged.

If I then draw a moderate current from the batteries (5-8A) the battery voltage drops down to 12.2V in a few hours and triggers the low voltage disconnect. Presumably I'm getting something less than 20AH capacity from 200AH of battery before hitting the 12.2 volt threshold. That doesn't sound right to me.

It been cold - say about 40F when I tested. I'm assuming that at 40F I should have been able to extract around 40% of the batteries capacity befor hitting 12.2V, but I'm only getting a fraction of that.

The batteries are a no-name 12v deep cycle battery that was presented as 'sealed' but in reality have flush screw-in caps for the cells. Actual brand is "Xpedition 31DCM deep cycle battery".

I dropped them down from under the coach and have them on the bench. Cells are full to within 1/8" or so of the fill marks. Specific gravity at 40F is 1.28-1.3.

I'd like advice on steps to take to determine if the batteries are working as expected or not. I.E. - if at 40F a lead acid battery only is expected to have 10% of it's labeled capacity then the batteries are good and I just need to move a thousand miles south.

If they are junk, I'll probably put new AGM's back underneath the coach and call it good. Getting at them is a PITA - it's not possible to reach the terminals or caps while they are mounted under the coach.

You would need to get a temp compensation allowance chart for the specific gravity, but I think that your readings are very close to full at 40*F.


Your actual capacity does seem very low, though, so something is not right. I think at 40*F you should have over 80% capacity.


I would start with a load test for reference although not the best for deep cycle battery testing, and then do a 20 hr rate, in amps, capacity test to 10.5v to see what you are really getting.



My bet is that the batteries are toast.