I applaud your efforts and your generousity in posting and i want to refine the information available to this community.
Standard replacement battery for a sansa clip zip is a 303038P, available from ebay, ali express, and possibly some battery specialty retailers even at this date (June 2018). The larger battery you have used might not allow you to close the case. If that is correct, an uncased mp3 player is more than I will pay for an extra 7% in battery life.
Good luckto you case -crackers everywhere.
