You can charge it each time without worrying about overcharge; however, unlike Ni-Cd packs, the amount of capacity remaining in the battery can easily be read with a simple voltmeter. A reading of 12V is essentially dead, and a reading of 13V is full. The discharge curve on these batteries is linear, therefore 12.75 volts means the battery still has 75% of its capacity remaining.

Never leave a lead acid pack discharged for an extended period of time, or sulfation will result. Basically, sulfuric acid in the electrolyte reacts with the lead to form lead sulfate. Lead sulfate is a poor conductor, which will cause your battery to become a very large paperweight.