Find a new Sidekick battery for your T-mobile sidekick.  Buying sidekick batteries from eBay is a smart choice.  You can get the same battery for your sidekick for about 60 dollars less than what T-mobile is going to charge you.  It is the same OEM sidekick battery, just without the overhead.  Replacement batteries are available for the Sidekick 3, the Sidekick LX, Sidekick 2008 and the sidekick Slide. Sometime they are also available for sidekick II and the original sidekick.

Sidekick Batteries for Sale