No worries. Also, if you know you're just going to be using cellular (e.g. you're on the move or whatever) , you should consider turning off WiFi.
Also, if you want to scrape the bottom of the barrel, you can also consider messing around with the screen brightness settings.
(If you're not running up to date software, you might contemplate that too, since they no doubt put some energy enhancement tweaks into their updates)
Edit to add: Have revised my comment about location services above, looking at the specs the iPad does indeed have GPS on the Wifi+cellular models.