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JaxDad

Greater Toronto Area

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Posted: 07/23/21 05:32pm Link  |  Quote  |  Print  |  Notify Moderator

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.

MEXICOWANDERER

las peñas, michoacan, mexico

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Posted: 07/23/21 05:42pm Link  |  Quote  |  Print  |  Notify Moderator

  • 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

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Posted: 07/23/21 05:44pm Link  |  Quote  |  Print  |  Notify Moderator

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

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Posted: 07/23/21 05:46pm Link  |  Quote  |  Print  |  Notify Moderator

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)


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

JaxDad

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Posted: 07/23/21 06:10pm Link  |  Quote  |  Print  |  Notify Moderator

MEXICOWANDERER wrote:

  • How old is the battery? 2 years old

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

  • It reads 12.5 volts but cannot sustain any type of load? 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? Instant.

  • Then returns to 12.5 volts once the load is removed?
Si, gracias.


JaxDad

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Posted: 07/23/21 06:12pm Link  |  Quote  |  Print  |  Notify Moderator

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

The Western States

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Posted: 07/23/21 06:22pm Link  |  Quote  |  Print  |  Notify Moderator

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.


2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
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Bob


NamMedevac 70

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Posted: 07/23/21 06:35pm Link  |  Quote  |  Print  |  Notify Moderator

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

* This post was edited 07/23/21 06:44pm by NamMedevac 70 *

JaxDad

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Posted: 07/23/21 07:38pm Link  |  Quote  |  Print  |  Notify Moderator

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

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Posted: 07/23/21 09:20pm Link  |  Quote  |  Print  |  Notify Moderator

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.

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