How did you manage to get unlimited for £9?To be honest once 3UK stop offering all u can eat (Which they never will this is the main selling point for 3UK) we move onto Virgin mobile unlimited package for £25.
For battery I haven't notice any difference between WIFI VS Cellular wifi i get around 9 hours usage and Cellular with full signal i get around 8hours and 30 minutes.
the main reason I use this much data is getting my moneys worth each month for £9 is a bargain.