PbCl (lead acid) batteries need to be kept fully charged. Overcharge cause damage, undercharge cause sulfasion of the electrodes. Your battery probably got damaged due to a failing alternator, and being flat for a while was the final straw. When you buy a new battery, it should be empty and then the shop fills it up with acid when you buy it. If they do not do this, then don't buy it. How do I know this? I'm an electronic engineer and had to do research the last 2 weeks into rechargable battery technologies.

By the way, with Ni-MH batteries as found in cell phones etc., you should fully discharge them once every 3 months. In between, don't care how you treat it. Fully discharge means run them 'till the phone turns off. With Ni-Cd run them flat once a month. Don't care in between. With both types you can then expect a life of 2 years. The original "memory effect" problem has been solved long ago, and full discharge is only required to break up crystal growth on the electrodes. Actually, full discharge reduce the life of the battery. so do it only evry 3 (or 1) months. Something else to do, a new battery should be charged at 10% of it's rated mA/h for 24 hours to equalize the cells, else you will never get the full capacity out of it. Just ask an electronics guy to do this using a power supply with current limiting, and do it only once. Hope this helps someone...