Still bulk charging after 2 days

[Saabpilot]

I recently purchased a camping trailer with 2 AGM batteries that were deeply discharged. I managed to get them to accept a charge however they won’t progress past the bulk charge phase on my smart chargers and continue taking the full 5 amp capacity.
The resting voltage of both is approx 12.6 volts and will not improve after 2 days. I would appreciate your advice on what to do before I assume they are unrecoverable.
Many thanks.

 

[gnubie]

What's the amp hour rating of the batteries? Are you charging them in series, parallel or separately?

 

[Saabpilot]

120 ah. I have separated them (previously parallel) and charging with 2, 5 amp smart chargers. Thanks

 

[gnubie]

With the charger connected to a single battery and charging for 24 hours, what is the voltage read at the battery's terminals with a multimeter? If you can measure the current into the battery too that'd help. A clamp meter would do the trick but you could use a standard meter in series in amp mode, if the meter can handle the current involved.

 

[Saabpilot]

12.6 volts. It is taking 5 amps which is the capacity of the charger

 

[gnubie]

120AH fully discharged is > 24 hours to recharge at 5A but if all is good the voltage should have risen above 12.6V by now considering you've been at this for over 2 days. You are still seeing 5A so we know that the battery is not badly sulphated nor 'dried out'. Can you check the voltage your charger is achieving, it might be tricky since it's a smart charger but try anyway - disconnect from the battery and measure the voltage from the charger with your multimeter.

Is the case of the battery getting warm in general or is there an area on the sides where it is noticably warmer than the surrounding areas?

 

[Saabpilot]

I have a Victron charger with Bluetooth so I can see it is around 13volts. Consistently 5 amps which I am concluding the battery is turning into heat and not electricity.
Is it possible to take it to a specialist to load test? Does that work for AGM batteries? Do I need a higher capacity charger? Right now I have disconnected one battery and plugged in my 12v fridge in the hope that cycling it will restore some capacity.

 

[gnubie]

A battery shop is just likely to slap a basic load tester on it that is designed for cranking batteries and tell you it's no good because it isn't designed for that purpose anyway... I'm assuming they are storage batteries not cranking batteries pressed in to storage service.

If it's a Victron charger we can largely rule that out as a problem unless a custom charge profile has been configured. Check your charger configuration to ensure it is set up for an AGM battery.

5A at 12V is 60 watts. It has to be going somewhere, that's either chemical reactions that raise the charge state of the battery, rapid splitting of electrolyte or heat. AGMs would be toast if gassing at that rate and the current quickly fall off as a result so that leaves either the battery is still actually charging, or it's getting quite warm. Batteries do warm up while charging but with 60 watts going somewhere it's going to have to get quite warm.

5A is an easy charge rate for a 120AH battery, in good condition. Sometimes damaged batteries can be bought back to life after a slow charge to raise the voltage up, by hitting them with short high current charging but they never regain full capacity. If the voltage has not risen over 12.6 after another 24 hours of charging I think you have a lost cause.

 

[Saabpilot]

Thanks for the advice. They are getting warm but not excessive. I have separated them for this reason. I will give it another 24 hours and see what happens. I think they are probably at end of life...

 

[Saabpilot]

I am tempted to jump them to an alternator for a short burst as you mention. Short meaning 5 minutes.

 

[Hedges]

I've had dead batteries (automotive starting) which took days to come up, and served me for a couple years.
It could be there are one or more low cells. The technical manual for my SunXtender AGM do describe an equalizing process which can be tried. Being sealed, you can't add water to replace anything lost, but it could be that equalizing at a suitably low rate lets it catalytically recombine.
Worth reading about the process and trying it.

 

[Saabpilot]

Thanks. I put both onto an alternator and they pull 15 and 28 amps on in turn. I’ll just let them soak for a few days and watch the temperatures. I’ll look up Sinextender to see what they say.. regards.

 

[gnubie]

Fingers crossed.

 

[Hedges]

Thanks. I put both onto an alternator and they pull 15 and 28 amps on in turn. I’ll just let them soak for a few days and watch the temperatures. I’ll look up Sinextender to see what they say.. regards.

That sounds like some place in Vegas.

Here's what I was referring to:

http://sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf