Several people have successfully documented replacing the built-in Lithium ion battery with a higher-capacity battery, increasing time the T3 can be used without charging. . Batteries of 1100mAh are available that fit just fine. However, disassembling the case is complicated by 5 small metal tabs, not mentioned by most online instruction pages: two on each side, and one on the back just above the docking connector, which must be released as one of the first disassembly steps (for example, by inserting a very thin shim and pushing it gently down, while pulling the bottom panel down enough to clear it).