A float charger should not allow the battery voltage to go above, say 13.8V, depending on the chemistry of the battery. Most cheap chargers are not regulated at all, and as the battery draw goes down, the voltage goes up. It is possible, with even a small charger, to cook a 14AHR battery over time, if it puts out more than the self-discharge rate of the battery. I like to monitor the voltage of a battery, with my trusty meter, so I know what exactly is going on...
