Make sure you buy a "float" charger not a trickle charger. Float charger drop the amperage to less than one amp once your battery is topped of at around 14 volts which is the correct charging voltage. "Trickle" chargers keep on delivering a small charge ( usually at 2 amps) even after your battery has topped off at 14 volts. 12 Volts is operating voltage BUT 14 volts is charging voltage. They are two different numbers.
People by error buy trickle chargers and cause battery damage. Schumacher is one of the biggest charging manufacturers and you will find this info on their web site. Very few manufacturers make float chargers/ maintainers. Be careful.