Repairing an old mobile phone battery is not successful. Battey is made up of many cells. You can not find exactly the cell is dead. In mobile phones, the battery is in form of a strip, not a cell. So you can not repair it. Only you need to replace it. I found someone is selling its battery. [link|https://www.amazon.com/Nokia-B002TJQTAU-Bl-5J/dp/B002TJQTAU/ref=sr_1_4?crid=T6D9G3GUCJW4&keywords=nokia+3310+battery&qid=1663229629&sprefix=nokia+3310+battery%2Caps%2C355&sr=8-4|Nokia 3310 battery|new_window=true].
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