Rechargeable Battery Stuff

[Ham]

I have a Garmin car GPS with a battery that's deader than a dead thing. Change it! I hear you say. Well, I did, for a chinese knock off. It lasted less than two weeks. It's a 3.7v Li-ion, 60 x 37 x 5 mm so much smaller than most phone batteries, I'm thinking of adapting it for an external battery pack. I assume the third lead is some kind of temperature sensor (Red=+, Black=-, green=sensor?).... anyone got thoughts on whether I need to consider the third lead to make it work? not worried about charging, it would just be nice to be able to hold standby, so you don't have to reset brightness each time it starts.

[Kim]

Third lead is usually to a thermistor (also connected to battery negative).  If not connected the device may decide the battery's on fire and shut down, or it may only care when charging.  You ought to be able to fake it with a suitable resistor.

[Ham]

So, measure the resistance on the (cold) duff Garmin, then add a similar value to my kludge?

[Kim]

Yup.   

[Ham]

Oh, and as a bye-the-bye, the full story.

I'd managed to get a <cough>genuine Garmin North America map onto my Garmin (having first verified that the OpenStreetMap .img file didn't work on it, as it does on my Oregon), to use in Mexico. I was glad I had, driving in Mexico can be fun and the Garmin routing and directions can really help. For example, where there is a road with two lanes in one direction, and one in the other. In the middle.  Anyhow, I'd successfully changed the battery before I left, so when it failed (symptom: restarts each power up, brightness set to 0 so unreadable, you have to set touch screen controls by memory, otherwise all as was) I thought I'd left the connection loose. So, in a supermarket I bought a set of watchmaker's screwdrivers for 50p, forgetting that the screws were mini-torx (anyone want a set of drivers for free? PM me). 

I then found me a nice little phone repair man (as you can imagine, stuff gets repaired over there) and over-stretched my Spanish beyond the point of comprehension, but managed to get the use of a small torx in the end. Only to find that all was connected.....