AGM battery question for the experts.

[JaxDad]

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]

The only reason I mentioned that "fix" in your particular specific diagnostic was to show a get-out-of-a-bind band-aid until a more suitable course can be arranged.

Mysterious breaks deep within a battery are doomed.

A high voltage screamer would help prevent high-potential disasters when aboard.

And an intrinsically limited charge maintainer self protects against runaway when a rig is unattended.

As far as connectors are concerned, the Concord Lifeline uses a Beryllium Copper post, which is much tougher than lead. I have no idea if other manufacturers offer the same level of protection. An L-Pad connector relies on a nut and bolt to clamp and if 316 stainless nuts and bolts are used corrosion becomes a non issue. Unnecessary post torque flex is avoided.

I believe Gdetrailer is referring to a charging device with power-supply quality output. Where disconnected, the device would limit noise *ripple* to say 20 millivolts maximum. Lifeline, demands this quality level of charger device right in their specifications.

[Gdetrailer]

PerryB67 wrote:
Or your WFCO fails and decides to run 21 volts to your AGM's.

Enjoy,

Perry

If a WFCO or any other converter hits 21 volts, you will have more other pressing issues than a silly AGM battery.

WFCO is not the only converter that can go sideways when it fails and voltages over 15V can destroy more than a battery.

Modern converters do not need or depend on a battery to regulate voltages either..

[PerryB67]

wa8yxm wrote:
There are a few different ways batteries fail
Shorted cell (they never hit 12 volts)
high resistance (What you got is very very high resistance)
and as Mex said broken conneciton (Also very very very high resistance)

Or your WFCO fails and decides to run 21 volts to your AGM's.

Enjoy,

Perry

[JaxDad]

Thanks to all, it was indeed toast, but like my brother Mex, I too have a passion for tinkering.

The wood screw trick did work, but since the battery is the power source for a PWC (that takes quite a pounding) it became a core against a new battery.

Despite repeated tornado alerts all afternoon, a couple of my nephews and their friends and me had a great day turning recycled dinosaurs into frothy water on Lake Simcoe (Google it) this afternoon.

Thank you again for the education. Now for a sponge bath of Voltaren……..

[time2roll]

Shot. Time to recycle it.

[wa8yxm]

There are a few different ways batteries fail
Shorted cell (they never hit 12 volts)
high resistance (What you got is very very high resistance)
and as Mex said broken conneciton (Also very very very high resistance)

It's toast. replace it .

NOTE this assumes you are measuring voltage at the battery. if you are using a volt meter INSIDE the RV clean all connections first the problem might not be the battery.

[MEXICOWANDERER]

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.

[Gdetrailer]

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.

[JaxDad]

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.

[NamMedevac_70]

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

[CA_Traveler]

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]

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]

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]

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)