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

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?
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.
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)
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.
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.
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.
NamMedevac_70
Explorer II
Jul 24, 2021
I just had a similar problem with a 12 volt AGM truck battery. Although fully charged it would not start the truck however my very small lithium Ion battery power brick/bank would strongly start the truck. After much failed troubleshooting I took it to auto repair shop and they replaced the battery end cables connecting to the battery post and this solved the problem. There was nothing wrong with the starter, alternator or 2 year old battery.

I have a marine start 12 volt battery in my second nearly identical Dodge Ram 1500 that has performed perfectly now for 3 years and is $80.00 less than a standard 12 volt wet cell bat. Check those battery cables connection terminals as mine were rotten. Voltmeter and multimeter and other checks on the cable ends falsely showed proper start voltage flowing from the battery to the starter. Your mileage may vary. This info may be of help to others with battery start problems.
Good luck
JaxDad
Explorer III
Jul 24, 2021
NamMedevac 70 wrote:
I just had a similar problem with a 12 volt AGM truck battery.

After much failed troubleshooting I took it to auto repair shop and they replaced the battery end cables connecting to the battery post and this solved the problem.

Check those battery cables connection terminals as mine were rotten. Voltmeter and multimeter and other checks on the cable ends falsely showed proper start voltage flowing from the battery to the starter. Your mileage may vary. This info may be of help to others with battery start problems.
Good luck

Cam oohn.

All my testing and results were with the battery out of the vessel and on a test bench.
Gdetrailer
Explorer III
Jul 24, 2021
JaxDad wrote:
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.

Not missing anything, its dead.

Battery has developed a high internal resistance for some reason, no load will read some voltage, add load and nada.

Typically not recoverable and especially since it is AGM where some tricks used on FLA sometimes breathes some life back in AGMs othe the other hand like their cousin Gelcells don't take kindly to abuse..

Just replace and go.
MEXICOWANDERER
Explorer
Jul 24, 2021
Several areas but a single diagnosis. Useless. A trade in core

At one of 12 plate to intercell or post junctions conductivity has been permanently compromised. But just for fun let's do this. It's fast and cheap.

Drill 1/8" and (2) 1/2" long sheet metal screws.
Drill a hole straight down into the terminal the depth of the screw.
This is lead so when you attempt to screw down into the terminal keep it in mind
It is soft and weak.
If you can run the screw down and tighten it then a bad connection may be temporarily bypassed.

If your drill emerged clean then stage 2 would be to try 3/4 length screws. But this would be the last gap. I am trying to soothe an unknown style battery.

If it does work, it works. Many UL style batteries use post top caps.

And this will provide entertainment.
I am guilty of trying to repair things.

Forum Discussion

AGM battery question for the experts.

About Technical Issues

Related Content

Battery Question??

Battery question

Battery Question

Battery Question

Battery/ charging question