Check or have checked the charging voltage from your alternator and also the main connections among alternator, starter and battery for corrosion or looseness. It is possible your system is overcharging. This can occur due to a bad voltage regulator and/or loose connections, including bad ground connections. You should with the engine running read a voltage around 14 volts at the battery terminals. If there are many electrical accessories on you may need to rev the engine up to about 2000 rpm to get a correct reading. If the voltage is closer to 15 volts than 14 that would indicate overcharging. Another indication would be if your battery is getting very hot or the elecrtrolyte fluid is boiling out, especially after a long drive.