That's the beauty of the Battery Tender and othes like it. They trickle charge when the voltage is down and stop when correct voltage is reached. Batteries like this situation much better than being drained and charged repeatedly and last much longer.
rapidblue wrote:how long would you leave a 1amp charger on a battery?
Just until the battery is fully charged, then stop charging it. This goes for any amperage or rate of charge. When it's full, it's full, and more charging is just going to heat and boil the electrolite.