My owners manual says:
"* Store and charge your batteries in a cool area. Temperatures below 50°F or above 100°F will shorten battery life.
* Never store batteries in a discharged condition. Recharge them immediately after they are discharged.
* All batteries gradually lose their charge. The higher the temperature the quicker they lose their charge. If you store your tool for long periods of time without using it, recharge the batteries every month or two. This practice will prolong battery life."
Batteries that have been sitting idle for a month probably would have enough charge left in them for you to use one while you recharge the other. I'm not sure if you'd gain anything by having them recharge everyday for 15 minutes and you might even damage the batteries by doing this. After all, how much of the charge would a battery lose overnight?
111,111,111 = 12,345,678,987, 654,321