Eneloops seconded. I was using lithium but with the runtime being just as long with these newer rechargeables I've been able to stop buying the lithium. I use my gps often so I just top them off when done and once a year put them through the analyze cycle in my charger (c9000) to test them.

Understand the implications of the almanac and the ephemeris.

Almanac: if you've not used the device for a few months, the device almanac may be out of date and it will benefit from being left on for 30 minutes so it can download a new one.

Ephemeris: this expires after a few hours; the time to download a new one is the reason a cold start takes 45 seconds or so. Moving the unit will this is happening can interrupt the download, so it's best to switch the unit on before you start travelling.