RE: Reconditioning large batteries?
No, once used up they are gone, plates inside give up, not the same as a nicad/nimh, however most are like your flight box battery (if its a smaller one so not to bad to replace, the bigger ones are kinda pricey and almost cheaper to replace the whole unit.
You could leave it plugged in with no load for 12hrs or so and see if it can catch up.