Revive a bad battery

Hi all, so my wife's Rav4's battery was getting weak during the winter so I just replaced it before things got worse and wife gets stranded.

I tested the old battery and it was not completely bad, some cells were getting "dry" so I added distilled water and I tried doing a "repair" using my Noco 10.

So far, health has been restored to 100%, but the internal resistance is more than 5mΩ.

How do I go about reducing it to lower than 5mΩ?

I have run the Noco 10 (repair mode) about 1 to 2x a day for more than a week now.

Thank you

 

I’d never trust that battery, it ain’t worth it. I’d dump it or turn it in for the core exchange. If you really trust it put it in your vehicle or back in hers and see how that works out. Dump it

 

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The problem with old lead acid batteries is gunk (that's the technical term) builds up on the plates. Once that happens you can charge it till the cows come home and it will only get a tiny bit better. But, youtube has a thousand videos on reviving old batteries so why not give one of them a try? You have nothing to lose cause that battery is already junk.

 

I didn't watch any of those videos but hear me out. The buildup is lead sulfate. Lead sulfate can be dissolved in a solution of sodium hydroxide. NaOH being a base, won't attack the lead plates.

Soooo, drain the battery, fill it up with NaO2 and water (mixed before filling it). Wait for the "gunk" to dissolve and finally refill with new electrolytes.

You can buy NaO2 crystals from home Depot in the plumbing section.

 

I say go for it! If the battery gets fuckered who cares? I guarantee you a battery can't get more fucked than mine and the battery place took it as a core without question. (yeah that's the battery from my wife's car. if you look close you can see the build up on the plates. https://www.tacomaworld.com/threads/the-battery-just-exploded.822906/#post-29512469/ )

 

DING DING DING DING! Tell'em what he's WON!
Absolutely! Yes.

We use to take our Deep Cycle Batteries from the boat to a guy that would rehabilitate them. This was around 1976.

He dumped the acid out. Flushed them with distilled water. I think he added some sort of solution to dissolve stuff? Maybe it was just baking soda? Then he would flush it out really well, add in new fresh acid and then trickle charge it up. Process took about a week.

But you could do that then because the EPA was in it's infancy and he was probably pouring all that down the drain. Also Deep Cycle has thicker lead plates and batteries were made differently then. More robust.
Now to get the CCA out of them to start a modern engine they have tons of thin, frail lead wafers in them that don't do well with all of that attention. Plus if you rinse a battery out now, you will see how much lead comes out in that process. It's not really plates as much as it is a screen that's lead plated. Once those screens warp and start touching you lose capacity to hold a charge. Once they start sloughing lead off in the acid they start losing the ability to take a charge.

I'll tell you this much. If you can do it in an environmentally responsible way... It is worth it to play with it and learn and try different things to see how close to original spec you can get it. Eventually rinse it clean and (USING EYE PRO) put an angle grinder on it and dissect it. But it is a tool for education now and not a tool for dependability.

 

And or the plates come lose from the gunk and crud

 

My luck has been around 50% with reviving weak batteries. Still worth taking a shot at it...
The first thing you should do is get a battery hydrometer and check the specific gravity of the electrolyte in all the cells. If one or two cells are way out of balance, then yeah, what everyone else here already said (lead sulfate most likely has shed from the plates in those cells, which cannot be recovered).

If the cells all check out the same though (within a few hundredths of each other), then I'd say stick it in your own truck and run it (not the wife's car though, just in the off-chance something does go wrong with it). The fact that it's at 12.91V (assuming that's after leaving it sit overnight) says the battery's health is pretty good. 5mΩ also doesn't seem bad for (what I assume is) a 24F-size flooded-type battery.

 

I honestly don’t get the point of all this. What are you gaining by trying to save a bad battery. You obviously don’t trust it since you won’t put it back in your wife’s car. If you put it in your vehicle you know there is a very good chance it will fail and will do so at a bad time when you really need it. Putting it in your truck is a crap shoot and you know it. I assume the battery is
3 to 5 years old or older and has reached its life expectancy. You already have batteries in your vehicles so there is really no need for this one anyway. Seems like a big time waste messing with the damn thing. At least bringing it back for the exchange value you get a couple bucks, maybe buy a 6 pack or two. Just dump it and spend your time doing something constructive or pleasurable.