How frequently should I charge the mouse?

It's difficult to tell from your profile or question which magic mouse you have. If it is the new magic mouse version 2, every month should be fine. It will last about 7 or 8 weeks on a full charge but if you forget it should remind you when it is down to 5 - 10%. If you still forget, you can put it on charge for 2-3 minutes and that will give you sufficient for 2 days average usage. Rechargeable batteries after the first few charges rarely last more than 12 - 14 days before you need to recharge them.

As it is required just like any other rechargeable device. The MM uses batteries, so it does not require recharging unless you use rechargeable batteries. MM2 has a built-in rechargeable battery.