don't overcharge a good battery... hydrogen gas is emitted and can cause an explosion...
one of the signs of a bad battery is increased internal resistance, which might account for the lower current and higher voltage. max voltage applied to the battery terminals should be 14.2, not 24, so you need to regulate that output voltage. also make sure when you recharge a battery, to 1)open the vent caps. 2)do it in a well ventilated area, and 3) put the battery in an open container like a plastic tub to contain any acid spills (accidents do happen). monitor the battery. if you hear fizzing or see hydrogen bubbles, disconnect the charger immediately (unplug the charger from the wall, do not just disconnect the clips which can cause a spark at the battery).