I have a used Mugen Power aftermarket replacement battery for Palm Pre/Pre+/Pre 2. From the factory this battery is rated at 3800mAh, as you can see from the screenshot, it's got 3547mAh left. This battery is larger than stock, so it comes with a replacement back cover, which has some pieces missing at the top. This aftermarket back is not Touchstone compatible.
Asking $25 OBO shipped within US, buyer to pay shipping worldwide.