Portable generators with electric starts use a 12-volt battery to start their engines. The batteries must be at a full charge to have enough power to start up the generator. When a generator is out of use for a long time, the battery begins to lose its charge.
If a generator battery loses power, recharging it is an option. A battery that has been stored for a long time without charging or has been subject to repeated deep discharges may start to lose power and not hold a full charge. Slowly recharging the battery can prevent this problem. It is also important to avoid overcharging it, which is another cause of damage to the battery.