The Samsung Galaxy S II ships with a 1,650mAh battery, but with this 1,900mAh chap you can squeeze even more life out of your super-smartphone on each charge. Great customer reviews on Amazon, and £8.99 delivered.
The Anker Samsung Galaxy S II battery is the same size as the stock effort, so you don’t need a new battery cover. Bonus.
(Thanks to chompyrud at HUKD)