Video : 
Car battery with a dead cell, It is a great car battery that I would like to get working again.
In this video I empty out the acid. Rinsing the cells with water ,and filtering the acid and refill it again.
I failed to get the battery back to life. But it was not because I did not try.
I see in the comments that me cleaning this in my bathtub raises quit some concern. All my household water goes to a very good treatment plant,, where my rain water does not.. we actually have to "wast water" systems to be able to treat the dirty water better.
Still the small amounts of lead, I wash out in definitely not recommendable. (But please keep in mind that lead is dug up from the ground.)
Here in Denmark there is a deposit on car batteries like this,, around $8 so I returned this to my mechanic, for him to deliver back. I just traded this one for another "not as bad" a battery.
Please see this failed experiment, and me shearing it, as a reason that no one else really needs to try this. It does not work.