A trickle charger slowly charges a battery. Trickle chargers are designed to add power to a battery at the same rate the battery discharges itself over short time periods. In this way, the battery charge can be sustained indefinitely, which is ideal for batteries that may not be used frequently, such as marine batteries. However, even though it delivers an extremely slow charge, some trickle charger models can only be connected to a battery about once a month for approximately two days to prevent damage to the battery cells and possibly cause a boilover of battery acid. Other trickle charger models, commonly referred to as floater chargers, can be connected to a battery indefinitely. Review the owner's manual to determine which type of charger you have before leaving it connected to a battery for more than a couple of days.
Set the switch on the front of the trickle charger to the correct voltage for the battery. For automobile, truck and most marine batteries, the setting will be 12 volts.
Scrub each post on the battery separately with a piece of steel wool to remove corrosion so the charger will get a better connection.
Connect the large black alligator clip on the end of one of the trickle charger cables to the negative (-) terminal on the battery.
Attach the red alligator clip on the end of the other cable to the battery's positive (+) terminal.
Plug the trickle charger into an electrical socket and switch it on.
Run a standard trickle charger for approximately two days, then disconnect for a month to prevent overcharging. Floater chargers can be connected indefinitely, although it is a good idea to check the battery at least once a month.
Check the owner's manual for your trickle charger to determine whether it is a floater type that can be left on for longer periods.
Do not scrub both battery posts with steel wool or anything else at the same time to avoid risk of shorting the battery and electrical shock.