That depends on whether it's the browser that's using that percentage. (BTW, that's percentage of the amount of power being used, not the percentage of the battery capacity - so if the browser is using 10%, and the total charge went down by 10%, the browser used only 1% of the battery capacity.) It can depend on other things - if you're using mobile data (not wifi) and the signal is weak, it's going to use a lot of battery for any data, not just browsing. (A weak signal coming in tells the phone that th tower is far away, so it increases its transmitter power so it can reach the tower. The weaker the signal, the more transmitter power from the phone - until you lose the connection when the signal is too weak in either direction.)