18650 Battery Powered Emergency/Survival Phone

I happen to have a phone which wouldn't charge the internal battery. This is where I got the idea to power it with an external battery. To save it from trash can and repurpose it in a way, give a second life.

Ever wanted a phone that you can take outdoors and use the same batteries as for flashlight? I did. You can just get a bunch of lithium 18650 batteries with you. As we all know, the batteries themselves can be salvaged from laptops and such. Unified rechargeable batteries are pretty convenient, right?

The phone is old and simple, so it has pretty low power consumption. Combine it with the ability to take a lot of energy with you and it makes a good emergency or maybe even survival phone. It is not waterproof however, but I'm not going to dip it in the water anyway.

Difficulty: low. Couple of hours to tie it all together.

Tools:

Soldering iron
Drill with 2mm bit
Hot glue, double sided tape
Cutting pliers
Better dremel or a file

Materials:

basically any phone that has battery close to 3.7V
18650 holder
18650 charger circuit (e.g. 03962a but not limited to)
2mm bolt and nut (will it fit your battery holder?)
scrap wires

Take a phone you would like to use, and try to power it with a battery. Most of them will work from external battery just fine.

Step 1: Make a Technological Access Port on the Side (a Hole)

Remove the battery and fit the charging circuit inside. It has to be accessible from the outside, right? Need a hole. You can use dremel or a file if you want it more clean, but I just cut the plastic with cutter pliers because I wanted it made quick!

Step 2: Mount the Battery Holder

The back cover on this phone happened to be metallic, which is good, because it will hold a tiny bolt better.

Drill a hole with the diameter of a bolt. I used 2mm one. Try not to bend it.
Also drill holes for wires.
Countersink it by hand with a bigger bit.
Apply hot glue and insert a bolt immediately. Or use a double sided tape instead of glue, it's to prevent sliding.

Step 3: Wiring

Wiring is as simple as on diagram - two wires to the battery, two wires to the phone terminals.

This is where you need to solder. Phone terminals would be better soldered too, but I have just wraped wire to them, works fine.

Also it is a good idea to fix charger PCB in place. Glue it, and also make a plastic stop to mechanically reinforce it when usb cable will push on it.

And looks like we are ready to close the back cover!