You can visit the nearest Nokia store and see if they still have a replacement battery available for the Nokia 6275i. But since this model has already been discontinued,
it is most likely that they don't. In this case, you can try to shop online.
Here are a couple of links to websites selling replacement batteries for the Nokia 6275i:
http://www.atbatt.com/product/6790/cellular/nokia/6275i/battery
http://www.easy-battery.com/mobile-phone-battery/nokia-6275i.php