Adding self charging to a Garmin StreetPilot III

WARNING, MAKE ANY MODIFICATIONS LIKE THIS AT YOUR OWN RISK. Garmin will likely void your warranty.

Adding charging to the Street Pilot 3 isn't too difficult, but you need to have reasonable soldering skills. You'll need to add a jumper wire with a diode and resistor inline. The wire, with resistor and diode inline, goes from the +12 input power line to the battery positive. Input power can be found on the board near the power connector as seen below.

Disassemble using the eight small screws on the back. The antenna can remain in place but power (the batteries) should be removed. Try not to disturb the rubber gasket between the case halves.

The battery power comes onto the main board through a screw. Battery positive comes onboard near the metal shield and goes directly to a large part (likely a diode) beside it. With care you can solder to this part.








So, you add a wire from the power input (red connector wire), to the ANODE of the diode that you add, through a resistor that you add, to the battery positive. You'll of course need to insulate the inline wire, diode & resistor that you add. Some small heat shrink works well.

The diode is any common diode like a 1N4001. ANODE on the 12 volt side and CATHODE towards the resistor side. (The cathode on the diode is normally marked with a stripe.)

The resistor you use will depend on the batteries you use, assuming 12 volts and 6 cells, NICAD or NIMH. Use the value closest to your batteries.

Battery capacity




82 ohm



68 ohm



47 ohm



33 ohm



27 ohm


This is a trickle charge. It takes about 14 hours to totally recharge the batteries. Avoid significant overcharging. NEVER charge non- NICAD or NIMH batteries as they may leak or explode.

When reassembling, make sure the gasket is still properly in place and don't tighten the screws too much as you may strip threads or distort the gasket.

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Last update 08/05/02