I will readily admit, I’m not a battery expert, let alone AGM batteries. I have a (to me) real puzzler, maybe it’s just chemistry I don’t understand. I have a ‘powersports’ battery, an ETX20L if it maters, that reads 12.5 volts at rest but drops to 0 when any load is applied.The really strange (to me) part is that once the load is removed the voltage rebounds to 12.5 volts.Once I try to charge it though it won’t take a charge since it’s already ‘charged’ at 12.5 volts. What am I missing here? Thanks in advance.

How old is the battery?Is this a 20 amp hour garden tractor size battery?It reads 12.5 volts but cannot sustain any type of load?Instant total loss of power?Then returns to 12.5 volts once the load is removed?

You have a bad connection somewhere inside the battery, that has very high resistance. When you are measuring the voltage with the meter, you aren't drawing any current, so there is no voltage drop across this bad connection. As soon as you load the battery, it is pulling current so there is voltage drop, which is why you see the voltage at the terminals drop to near zero. This is probably not recoverable.

JaxDad,Voltage without a load is pretty meaningless. Find an old "dumb" charger and try to recharge this battery. (and no, I'm not an expert)

MEXICOWANDERER wrote:How old is the battery? [COLOR=]2 years oldIs this a 20 amp hour garden tractor size battery? [COLOR=]Pretty much, but for a PWC in this case.It reads 12.5 volts but cannot sustain any type of load? [COLOR=]Very low amperage loads yes, LED light, xenon strobe, yes, good old fashioned carbon pile load tester, crashes faster than a millennial texting while driving. Instant total loss of power? [COLOR=]Instant.Then returns to 12.5 volts once the load is removed? [COLOR=]Si, gracias.

pianotuna wrote:JaxDad,Voltage without a load is pretty meaningless. Find an old "dumb" charger and try to recharge this battery. (and no, I'm not an expert)I can relate to old & dumb, thanks, I hadn’t thought of that angle.At this point I’ll even take suggestions from someone who stayed at a Holiday Inn Express.

AGM battery question for the experts. | Good Sam Community

CA_Traveler
Explorer III
Jul 24, 2021
Take it to a good battery store and have it load tested. A auto store is not a good battery store.

BTW 12.5V is not 100% charged, more like 12.7-12.8V. Should to to 13.4V float with a charger if not 14.4V, but check your battery specs. Yours sounds like toast.
JaxDad
Explorer III
Jul 24, 2021
pianotuna wrote:
JaxDad,

Voltage without a load is pretty meaningless. Find an old "dumb" charger and try to recharge this battery. (and no, I'm not an expert)

I can relate to old & dumb, thanks, I hadn’t thought of that angle.

At this point I’ll even take suggestions from someone who stayed at a Holiday Inn Express.
JaxDad
Explorer III
Jul 24, 2021
MEXICOWANDERER wrote:
How old is the battery? [COLOR=]2 years old

Is this a 20 amp hour garden tractor size battery? [COLOR=]Pretty much, but for a PWC in this case.

It reads 12.5 volts but cannot sustain any type of load? [COLOR=]Very low amperage loads yes, LED light, xenon strobe, yes, good old fashioned carbon pile load tester, crashes faster than a millennial texting while driving.

Instant total loss of power? [COLOR=]Instant.

Then returns to 12.5 volts once the load is removed?
[COLOR=]Si, gracias.
pianotuna
Nomad III
Jul 23, 2021
JaxDad,

Voltage without a load is pretty meaningless. Find an old "dumb" charger and try to recharge this battery. (and no, I'm not an expert)
FWC
Explorer
Jul 23, 2021
You have a bad connection somewhere inside the battery, that has very high resistance. When you are measuring the voltage with the meter, you aren't drawing any current, so there is no voltage drop across this bad connection. As soon as you load the battery, it is pulling current so there is voltage drop, which is why you see the voltage at the terminals drop to near zero.

This is probably not recoverable.
MEXICOWANDERER
Explorer
Jul 23, 2021
How old is the battery?
Is this a 20 amp hour garden tractor size battery?
It reads 12.5 volts but cannot sustain any type of load?
Instant total loss of power?
Then returns to 12.5 volts once the load is removed?

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