Cellphone Lithium Battery with 3.5 mm Jack

The 3.7 V Li-ion battery used by cellphones has a good shelf life, is compact and lightweight, and charges quickly with little degradation.  Its voltage is pretty compatible with devices that normally accept two AA alkaline batteries, and so it's a natural substitute.

This instructable describes how to attach a 3.5 mm audio jack to a cellphone battery, allowing it to be connected to a headlamp that has a 3.5 mm receptacle.  Such jacks and receptacles can be scavenged from broken audio headphones and radios by desoldering their leads.

A particular detail is the creation of a custom shrink-fit sleeve for the battery using a polyethylene terephthalate (PET) water bottle.

Step 1 Materials and Equipment

Here are the things I used, minus the soldering stuff, cardboard and heat gun.  PET plastic will shrink under a heat gun, but not enough with a hair dryer or boiling water.  You'll also need pliers, wire cutters/strippers and maybe a knife.

Comments

[mguima]

I think that there are no such a earphone signal labeled "mix".

The four wires in the plug are two for each earplug: Positive left, Positive Right, Negative Left, Negative Right. The two negatives are both attached to the plug base contact. Positives go to the middle and the tip.

Change the wire is a good idea. The original audio wires from the earphone are very thin, so, their resistance is not negligible, and you would waste battery power in the wire.

[DanYHKim]

Thank you. That makes a lot of sense. I will be sure to use suitably thick wire.