how can i change the battery
battery voltage is too low to save tm-d4000 data
If you know anybody who builds computers, it is not difficult to open up the TM-D4000 to replace the battery. It's the same battery as most computer motherboards.
A small disk shaped watch battery which can be purchased at radio shack or electronics store. But if you are unfamiliar with this, try to get help from a technician.