AGM battery rejuvination

rocketbob · #1 03-16-2014, 08:39 PM

My C150 needed a new battery and rather than going with another old-school lead-acid battery like the Gill that was in it I started looking at Concordes. I realized that I had an old one on the shelf that was replaced in my RV after ten years of service. At the time of replacement it was fairly weak. It had been sitting on the shelf for over four years so for giggles I charged it and put it in the 150 since it was the FAA/PMA'ed battery. No dice when I tried to turn it over.

So for additional giggles I decided to see if I could revive it.

While the harshest winter I ever recall carried on I tried various charging techniques along with small desulfator purchased on eBay. Not much improvement. So the google answer machine was called in to help and I discovered some scant postings of people who were successful with rewetting the cells of AGM batteries with store-bought electrolyte. Popping the lid off the Concorde revealed some screwed-on vents. After opening the vents and looking inside I was surprised at the amount of junk floating around on top of the cells. I took the battery outside and shook it to dump the junk out. Then came a trip to the auto parts store and I came home with a 1.5 gallons of electrolyte purchased for $13 and filled up the battery full, let it sit for 30 minutes, then emptied the electrolyte, and recharged.

To my great surprise it now performs well, and stays charged over 12.6V or so even after sitting for a few weeks.

I have a couple of Odysseys on the shelf and I popped the cover off one to see if the same thing could be done. Most certainly doable but one would have to use a large syringe to rewet the cells.

So if you have an old Odyssey that lost its mojo I suggest you try this experiment and report back.

rzbill · #2 03-17-2014, 03:08 AM

Thanks Bob,
I have a dead PC680 that I would like to use in a 73 beemer that I am putting back together. I will let you know how it goes. Not too soon though. The build is not high priority

aerhed · #3 03-17-2014, 08:10 AM

I have a 2 year old Gill that I installed brand new and let sit for 3 months. When spring came it was totally dead. I pulled the caps and it was bone dry. Added a splash of electrolyte and charged it. Appears to have taken a charge and held it, but I haven't load tested it. I will now. Thanks Bobber.