Back in the day this was even better:
Original Galaxy S battery was getting weak? Order a new battery from Amazon for 13€. Battery arrives, pop the back of the phone off, pull battery out (just like that, no soldering), push new battery in. Push the back of the phone back on, done.
New battery in and it had more mAh than the original one. Despite overclocking that phone it ran a day longer after the replacement.