A lead acid battery at 12.4 volts is discharged. Full charge is 12.85 volts. Most all cars need a good battery to start and energize the alternator. Electronic ign. needs good power as well. A battery below 12 volts is considered dead. A new battery needs to be charged with a constant current charger. The initial charge is the most important. The first charge will determine what the memory is. If you use a constant voltage charger (automatic) initially, what ever the charge is, is all that it will ever be. Example, 80% first charge, the battery thinks that is 100%. Thus poor longevity and performance. Once a battery is in question, replace it. Each time a discharge takes place, it shortens the life. Hope that helps.