Lead batteries can be rejuvenated, with a device mostly called "A pulser/desulfator/refresher" Short story: I had a completely dead 12V car battery. It was at 0V and would not accept a charge at all. Connected it to a bench power supply and slowly cranked the voltage up until it charged with a couple mA @ 30V. Slowly it accepted more amps so I constantly dialed the voltage down until it was charging at 14volts. Then hooked up the desulfator and left it for couple of weeks. Every other day checked voltage and hooked it up to a charger for couple hours. After that it was perfectly able to start my car(oldtimer) again.