Mission Impossible? Recharging a 2019 AGM 12V battery showing 1.3 volts.

softdown

Transmission fluid change on Prius went sideways - rounded out extremely tight 10mm female hex. Amazon took full month to ship removal tool. Lowes wanted double the price of Amazon. Seat belt prevented door from closing - I thought it was flex from being jacked up. This killed the battery.

2019 AGM 12V starter battery discharged to 1.3 volts. Four modern chargers failed to initiate the charge process. A 1990's 10 amp charger is slowly bringing up the voltage however. It is feeding the battery a 16ish volt charge with, I would guess, very low amps. After approx. 8 hours the battery is showing 5.3 volts with the charger disconnected. The voltage did not plummet while the charger was disconnected overnight.

It gets far more complicated than that of course - this is my life we are talking about. It is - interesting. This battery reconditioning is supposed to be futile. But why not persevere - see what happens.

Marc Kurth

Our standard deep discharge recovery procedure for Sun Xtender and Lifeline AGM batteries:

1) Using a constant current charger set for 5% of the battery C/20 capacity, with the maximum voltage set to 18v.

2) When the charge voltage climbs to 15.5v, continue for 4 more hours.

3) Discontinue if battery temp exceeds 130F. Allow it cool, then continue where you left off.

4) Run a capacity test.

 Fully recharge the battery, then equalize at 15.5v for 6 hours if needed.

We have brought back 100's of batteries that were condemned as unrecoverable.  About the best that I see, is 80% of original capacity, which is better than zero. Yours may well be recycle material.

I have seen customers "redneck" this procedure using a large old school farm/ranch type manual charger. The 200 amp boot setting will often get you close to 17.5v, but you have to babysit it.

Marc

softdown

The old charger bought it up to 9 volts before I switched to a 4 amp charger set on AGM charging. So I don't have to worry about cooking the battery while I sleep. Seem to have cooked a little ATV AGM battery using a charger set on lithium charging. The little battery was 7 years old and worse for wear. Thought I could maybe rejuvenate it a bit. Instead a couple sides bulged and the battery died.

I'll try the lithium setting (higher voltage) if I can get the battery over 12.6 volts resting. Think it has a slim chance being a 2019.

BB.

With the battery below "charging setpoint" (like below 14.x volts), the actual charger voltage does not matter... Just the rate of charge. Following Mark's C/20 5% rate of charge, the battery's actual voltage will not rise above 14.x volts until it is near full (i.e., if 18 volt charger and battery is only at 5% current and 10 volts--It is charging at 10 volts).

Many chargers will not start charging until there is ~9+ volts on the battery. A "simple" charger may not care and will start at 1 volt...

I did have a "simple" 1 amp cube 12 volt charger and it worked... HOWEVER, when charging the (at the moment) "dead" battery (only a few volts), the charger itself overheated and popped open the plastic case (still worked, surprisingly).

-Bill

softdown

Charged up to 12.9 volts with charger freshly disconnected. Not great but OK.

Battery tester advises me to REPLACE if a FLA and GOOD if an AGM. Curious since both settings call the battery 44% Healthy. A 500CCA battery showing 367CCA - enough for a Prius I think. But how long will it last?

Internal resistance is quite high - 8.1.

Now I debate putting a 4 amp charger using Lithium (high voltage) setting. Or simply replacing the AGM with the same size FLA - which I bought for the genset. Then the genset battery decided it was still "GOOD" once the temperatures warmed up.

softdown

Trying a compromise at the moment - A Duracell 4 amp charger set for FLA batteries. Not going to be here to babysit it for a bit. This charger considers the battery less than 75% charged. May be interesting. Or not.

I think Marc is accustomed to working with ~$600, or more, Deep Cycle batteries. That are worth babysitting. I'd place the value of this battery at closer to $40 or so. Could be no more than scrap value in fact.

softdown

Couple hours with the Duracell:

13 volts

396 CCA

51% HEALTHY

7.8 Internal Resistance

Still less than 75% charged according to this lil magic box.

Slight improvements across the board. It is warm inside the car - that also improves battery stats of course.

softdown

Lithium (higher voltage) charge setting has bought CCA up to 426. I'll leave it charging at that higher voltage for another hour. Then see what we have tomorrow. Don't want it to go sideways while I am sleeping. Looks like the battery is retrievable - if the voltage doesn't fall too much overnight.

This has been quite interesting. Almost everything I have been taught eventually proves to be - wrong. More or less.

I don't know how many times I have read that sub 10 volts destroys the battery - but the number is high. Then again, this battery may be dead in the morning.

mike95490

It will last till you are ready to leave the mall to go home tomorrow. and then will be dead.  Will test fine in the AM.   Have fun.

softdown

mike95490 said:

It will last till you are ready to leave the mall to go home tomorrow. and then will be dead.  Will test fine in the AM.   Have fun.

You are way optimistic. This is what I foresee. Somewhere in Georgia - in between my Colorado residence and my Florida rentals that are constantly getting torn up - the battery fails to a point that the hatchback won't even open. Hundreds of pounds of maintenance supplies prevent access from the side door. I see a congregation of alligators and eagerly feed them - by running into the swamp and flailing wildly. 

softdown

40F at 6am - battery shows 424CCA. It was 500CCA when new.  Nothing significant happened overnight. Will complete charge at lithium (higher voltage) setting. I think it will be OK though service life will be shortened.

For some reason this battery size has a high internal resistance. Even the new model has high internal resistance. The resistance is coming down with further charging.

softdown

Done some driving - 500CCA battery now shows 495CCA and is rated 80% healthy. Resistance has declined to 6 - it was likely ~5 when new. Being a 2019 - think I'll be OK.

Still can't believe it discharged to 1.3 volts. Took a very long time to recharge.

softdown

Prius are weird. Hooked up the teardrop camper yesterday for a trial run. Turn signals work but running lights do not. Suspecting a ground issue. I installed trailer electronics made for the Prius so this issue comes as a surprise,

Was startled to see the dash lights still on this morning. Accidentally brushed the gas pedal while trying to get the lights to turn off. The engine instantly roared to life. I can't hear a thing when it is idling.

Turns itself off when I leave for a few seconds to open or close the gate. But not last night! Prius are weird.