There are several causes, which can cause weakening of car battery. If you know these and maintain your car battery, it can improve the battery life. Things that cause battery weakening or failure are like:
• Massive use of battery power for lightning, air-conditioning, music system can make your battery weak
• Rash driving
• Low charge and acid stratification
• Using air-conditioner, lights and music system, when car is in idle condition
• Factory/manufacturing defects.