Assuming you have lost your TOMTOM charger, like I have. You may be in need of a temporary fix until your new one comes in the mail for the grand total of about $60 (Shipping, taxes, exchanger rate, ...). This instructable will tell you how to rig something up that will charge your watch using an old USB cable and an elastic band.

You'll need:

A USB cable
An elastic band
A wire cutter/stripper
A voltmeter to check the polarity of your USB cable leads.
A soldering iron to tin the ends of your stripped USB cable.

This instructable was written for the TomTom Runner Cardio GPS Watch, but probably applies to all of the TOMTOM GPS watches.

Step 1: USB Cable

Take your USB cable and cut the non computer connection end off. Then strip the cable so you have the wires exposed. Strip the individual wires too. If you can guess which is the +5 and Gnd wires, do those first.

Now put a Volt meter on the cable and make sure you know which lead is +5 and which is Gnd. On my cable, red was ground, and black was +5V. That's totally backwards to any cable I've ever seen, maybe that's why it was free? Regardless, that's why you want to use a voltmeter to check the polarity.

Now is probably a good time to pull your trusty soldering iron and tin the ends. I found putting a bit of ball of solder on the end of each of the two wires helps in making contact to the watch connections in the next step.

Step 2: Connect the Leads to the Watch

If you're looking at the back of the watch, the positive power is the large pad on the left, and the ground is the large pad on the far right.

Wrap an elastic around the watch and put several wraps over the leads so the elastic is nice and tight and will hold the leads onto the pads.

I slipped a screw driver under the elastic, and then slid the wire into place under the elastic. Remember it's positive to the left pad, and negative to the right pad. Connect the negative lead, and ensure you have a decent contact between the both leads and the pads.

If you're successful, you should see the watch start, and you'll see the battery icon showing that it's charging. If so, you're in good shape.