Hi All,I have 2 70AH 12v batteries conected for ~140AH @ 12v. I have a 10A charger on them overnight and it still says about 4A going in at 15v . I'm thinking these batteries are no longer taking a charge. One battery was half empty when I got the rig so I filled it with distilled water and charged it. Both batteries on resting read about 12.8v which indicates they are charged. Hooking up the charger to top them off I would think the amps would drop down to a trickle in a short time, couple hours? The charge started at about 8A and has tapered down to about 4A and not falling any lower. What are your thoughts?Greg

You need to charge them individually and test them individually. You will then know if one or both batteries are bad.

Allowing a battery to go that dry is not good for it. You can try an equalization charge for a few hours.

Lead/Acid batteries do not play well in parallel.As DonDat said, you have to charge them separately. What he neglected to say was that to get full power out of them, you always have to charge them separately. If you get get them charged, and one is weak, don't replace just that one. You will never get the two different batteries to share the load. Your best bet would be to get a pair of 6V golf cart batteries and connect them in series. You will get much better results.Matt

Matt_Colie wrote:Lead/Acid batteries do not play well in parallel.As DonDat said, you have to charge them separately. What he neglected to say was that to get full power out of them, you always have to charge them separately.Batteries play just fine in parallel. With the OP's problem it would be good to charge them separately to isolate his problem. Under normal circumstances, there is absolutely no reason not to charge batteries in parallel together. I don't know where this misleading information comes from but it is utterly false. The SG readings of my series/parallel battery bank are spot on with each battery. I charge them ALL at the same time everytime.

Waitin2Retire wrote:Hi All,I have 2 70AH 12v batteries conected for ~140AH @ 12v. I have a 10A charger on them overnight and it still says about 4A going in at 15v . I'm thinking these batteries are no longer taking a charge. One battery was half empty when I got the rig so I filled it with distilled water and charged it. Both batteries on resting read about 12.8v which indicates they are charged. Hooking up the charger to top them off I would think the amps would drop down to a trickle in a short time, couple hours? The charge started at about 8A and has tapered down to about 4A and not falling any lower. What are your thoughts?GregYou need to check their SGs and also note over time that the 4a stall is going on, whether the SG has stopped rising. If SG has stopped rising, then the charger is just making bubbles.Is it stalled at 15v too? With a manual charger it should keep rising to the point the charger runs out of steam to get it higher on that size of battery. Would expect 16+v with the 10amper on 140AH Heftier charger, higher voltage it can force the battery to. Yes, separate them where you suspect one is in worse shape so you can tell which one. Once both as full as you can get them, get a load test done on each one.

Are my batteries shot? Charging question | Good Sam Community

11 Replies

MEXICOWANDERER
Explorer
Sep 28, 2013
The construction of golf car AGM batteries is exactly the same as for their version of cyclable AGM batteries. Divide price by ampere hours. Pick the battery size that jams in best.

The AGM batteries can charge much faster. If I had 200 ampere hours of AGM located fifteen feet away from the alternator I would use no smaller than FOUR GAUGE WIRE, directly from the alternator output stud, through a battery separator then to a breaker and run directly to the battery bank. This is for usage where alternator charging was the primary means of recharging other than by generator and "converter".
time2roll
Nomad
Sep 28, 2013
You might get by fine on the one battery depending on use.
May as well use it hard and use it up.
westend
Explorer
Sep 28, 2013
Waitin2Retire wrote:
UPDATE;
I separated the batteries. I hooked the suspected good one up to the Trimetric by itself and it's fine. Good voltage and reads full.I guess the one that was dry when I got it is shot. Was hoping to finish the season out on these and go new in the spring. Looks like that won't happen. I'm considering a pair of 6v AGM's. Are these happy with the engine alternator charging while on the road or is that too much voltage for them? Thanks everyone for your help!
Greg

2013 GMC 3500HD, 10' AKC.
AGM's will not be hurt with your chassis alternator. That said, I wouldn't rely solely on the alternator for charging on a long term basis. You will get more longevity if you charge the AGM's with a standalone charger.
westend
Explorer
Sep 28, 2013
MEXICOWANDERER wrote:
Unknown age
Unknown type
Same or different brand?
Unknown in-service performance
Premature conclusions
Could add unknown charger and operational characteristics of same to the list.
Waitin2Retire
Explorer
Sep 28, 2013
UPDATE;
I separated the batteries. I hooked the suspected good one up to the Trimetric by itself and it's fine. Good voltage and reads full.I guess the one that was dry when I got it is shot. Was hoping to finish the season out on these and go new in the spring. Looks like that won't happen. I'm considering a pair of 6v AGM's. Are these happy with the engine alternator charging while on the road or is that too much voltage for them? Thanks everyone for your help!
Greg

2013 GMC 3500HD, 10' AKC.
MEXICOWANDERER
Explorer
Sep 28, 2013
Unknown age
Unknown type
Same or different brand?
Unknown in-service performance
Premature conclusions
BFL13
Explorer II
Sep 28, 2013
Waitin2Retire wrote:
Hi All,
I have 2 70AH 12v batteries conected for ~140AH @ 12v. I have a 10A charger on them overnight and it still says about 4A going in at 15v . I'm thinking these batteries are no longer taking a charge. One battery was half empty when I got the rig so I filled it with distilled water and charged it. Both batteries on resting read about 12.8v which indicates they are charged. Hooking up the charger to top them off I would think the amps would drop down to a trickle in a short time, couple hours? The charge started at about 8A and has tapered down to about 4A and not falling any lower. What are your thoughts?
Greg

You need to check their SGs and also note over time that the 4a stall is going on, whether the SG has stopped rising. If SG has stopped rising, then the charger is just making bubbles.

Is it stalled at 15v too? With a manual charger it should keep rising to the point the charger runs out of steam to get it higher on that size of battery. Would expect 16+v with the 10amper on 140AH Heftier charger, higher voltage it can force the battery to.

Yes, separate them where you suspect one is in worse shape so you can tell which one. Once both as full as you can get them, get a load test done on each one.
mena661
Explorer
Sep 28, 2013
Matt_Colie wrote:
Lead/Acid batteries do not play well in parallel.
As DonDat said, you have to charge them separately. What he neglected to say was that to get full power out of them, you always have to charge them separately.
Batteries play just fine in parallel. With the OP's problem it would be good to charge them separately to isolate his problem. Under normal circumstances, there is absolutely no reason not to charge batteries in parallel together. I don't know where this misleading information comes from but it is utterly false. The SG readings of my series/parallel battery bank are spot on with each battery. I charge them ALL at the same time everytime.
Matt_Colie
Explorer II
Sep 28, 2013
Lead/Acid batteries do not play well in parallel.
As DonDat said, you have to charge them separately. What he neglected to say was that to get full power out of them, you always have to charge them separately.

If you get get them charged, and one is weak, don't replace just that one. You will never get the two different batteries to share the load. Your best bet would be to get a pair of 6V golf cart batteries and connect them in series. You will get much better results.

Matt
2oldman
Explorer II
Sep 28, 2013
Allowing a battery to go that dry is not good for it. You can try an equalization charge for a few hours.