You might have some old useless phone batteries in your home. You can think it is useless, but you can reuse it in to a nice LI-battery. In this instructable, I used my old Galaxy 1 Battery.
Step 1: Remove Battery Sticker
There might be a sticker back on the battery. You can rip it out, and you can find the driver holes. It may be hard to rip it without making sticky stuffs, so use your finger to rip it out.
Step 2: Untie the Screws
Untie the screws that you just have found in the previous step. It will be very easy.
Step 3: Disassemble the Battery
If you disassemble the battery, you might see a PCB charging circuit. Look carefully and find some charging pins. You can read the pin's usage.
Step 4: Soldering
Sorry, I forgot to take picture while soldering.^^;
Solder the pins with some jumper cables. It doesn't have to be very long.
After that, cover it with some shrinkable tubes. It will shrinks when it meets fire.
Step 5: Making a Hole for Cables
In this step, you have to make a hole with an auto-driver. You have to make two holes for each jumper cables.
Step 6: Assemble!
Now, assemble the battery pack.
Be careful with the holes that you made. You should not take apart the cables.
Step 7: Choose Connectors
Choose a connector for your battery pack cables. In my case, I used a 3-hole connector.(But it has only 2 pins work for.) You can choose what you need for your projects. Micro usb cable is also okay.
Step 8: Done! Power Some MCUs
Now, you are done. Use your battery pack for your project. I used it for TI's MCU.