[EDIT: Sorry, replies came in while I took a break to finish sealing some cabinetry. Hopefully something below will still be useful...]
Do you think that battery recharging trick would work on my Etrex20x?
Hi Matt! I realized you addressed your question to mickeg, but I hope he won't mind if I take a stab at it.
While I don't have your Etrex20x model, I do know that on my Oregon 600t, Garmin offers a rechargeable battery pack. However, with many high-capacity Eneloop XX/Eneloop Pro cells in reserve, I preferred to use them.
Before going further, I should really stress that Garmin actively discourages the use of rechargeable batteries other than their own. On my unit, they very explicitly warn:
NOTICE! Do not attempt to use the device to charge a battery that was not provided by GarminŽ. Attempting to charge a battery that was not provided by Garmin can damage the device and void the warranty.
Source:
http://www8.garmin.com/manuals/webhelp/oregon6xx/EN-US/GUID-3954A785-E19A-4195-A79A-BA05FA168A9D.htmlIf you try the following, you're on your own if problems develop. Although I've had success, I can't endorse the method.
Open the battery compartment on your Garmin and look to see if there is a black rubber button under the batteries (photo below). It is an interlock switch depressed by the original Garmin rechargeable battery pack. When depressed, it tells the unit to allow recharging of suitable batteries. It is possible to take a bit of stiff plastic (as used on battery blister-packaging) and place it under some Eneloops to allow charging. You can see how the Garmin pack depresses the button here:
http://www8.garmin.com/manuals/webhelp/oregon6xx/EN-US/GUID-02E8CDAE-3929-43C6-91F2-9A9EF759EB80.htmlIt works, but should it?
Well...
1) You're going against Garmin's express recommendations, so if something goes wrong you may end up with an inoperable unit. It is now a technique commonly in use, but if Garmin figures out why, you'll lose your warranty coverage.
2) I determined it was worth the risk, tried it, and had no bad result to date.
3) The Garmin's internal circuitry is painfully slow compared to (Sanyo, now Panasonic) Eneloop chargers, so after all this, I prefer to use my Eneloop USB AA/AAA chargers instead and simply swap in new pairs of charged batteries. However, when coming toward the end of a charge, I have used this dodge to plug in my external battery pack or solar panel's accumulator battery and so get a bit more tracking done at the end of long days in the saddle (with careful management of screen options and a fresh pair of Eneloop XX/Pro AA cells, I have managed 17 hours of continuous tracking). My on-bike charging setups don't put out enough juice to simultaneously power *and* charge my Oregon 600T.
Regardless of which batteries you use, be sure to select the appropriate power option from your Garmin menu so you can maximize displayed battery life. Most Garmin units allow you to select between Alkaline (disposable), lithium (disposable, good for cold weather), or lithium-ion (rechargeable) batteries. Battery options may vary by model. Making the appropriate selection really does make a difference to overall displayed battery life.
Long term, Garmin's battery tabs sometimes fracture with frequent battery changes (metal fatigue, it has happened to me early on with my 400T). The trick to avoid this is to insert the battery's positive (+) pole first, the opposite of usual practice.
Circling back to your original question, Matt, if your eTrex lacks the rubber button under the batteries (I think it is missing for yours), it is unlikely you'll be able to charge batteries in the unit. A preferable way to do it would be to charge the batteries externally and perhaps power your GPS while underway using a buffer/cache battery to maintain power while stopped briefly or riding too slowly to maintain an adequate charge (and to avoid having to manually reset the GPS). The layout is like this: Hub dynamo > charging unit > buffer battery > GPS.
Best,
Dan.