The difference between a Battery Tender (Float Charger) and a Battery Charger (Trickle Charger)
The Battery Tender will only turn on and charge your battery when it has self-discharged below a certain level, whereas…
a Battery Trickle Charger continuously emits a small current of electricity regardless of the charge level or even if it’s full.
If you had a lithium-ion battery (like on a cell phone), this wouldn’t be a problem. However, if you’re dealing with a lead-acid battery (sealed, or otherwise) like in your car, motorcycle, golf-cart, lawnmower, boat, or battery bank, you’re at very high risk of damaging your batteries in the long-term if you leave them hooked up to a trickle charger. Trickle chargers that are on the cheap end of the spectrum can even destroy batteries overnight if left connected.
A float charger is significantly different from a trickle charger in that it will top off a battery at 100%, cease further charging and remain on standby. As the battery naturally loses charge over time, the float charger will once again resume its charging to top the battery off and then switch to standby mode. Due to this, batteries can be left hooked-up to a float charger for an indefinite period of time. Batteries work best when they are maintained at 100%, and a float charger is a perfect way to do this.