The cheap “trickle chargers” are junk, and are nothing more than a step down transformer and a diode...they will cook your battery.
You need to buy a “smart charger” that has electronics that know when to just maintain a charge by just floating at a very, very low current. Those will not “cook” your battery by overcharging it.
Battery Tender or a Marine Pro Charger are the ones I would buy. They start at about 30.00 and go up fo 200.00
