I’ve been trying to find the best batteries for a small handheld GPS that I use. This is a Garmin Geko 201, which I chose for its miniscule size and weight.
I used a data logger to measure battery voltage with the GPS unit sitting on a window-sill where it has a partial view of the sky. However I was concerned that the measurements are a bit unreliable since the GPS flashes a low battery warning and turns itself off when it thinks the battery is too low. Also it may be possible that varying satellite positions may affect power consumption, particularly as I have the GPS set to use EGNOS (Euro WAAS) which may depend on which satellites are in view.
So instead of using the GPS to measure battery performance I decided to use a torch (flashlight in USian). The nearest one to hand was a Peli Versabrite. (6000 CP, 5 Lumens, 2xAA, 0.6A, 1.8W). I used AAA batteries instead of AA since the GPS takes AAA batteries.
Battery life measurements
2 x AAA in Peli Versabrite.
Here’s the results.
- Light output drops to zero when the voltage drops below 1V.
- Current drawn is around 0.34A (not 0.6A per spec.)
- Measurements were over several days. Temperatures varied.
- 600 mAh NiMH had been through more charge cycles than the 750.
- Only one measurement of each type, not statistically valid?
- Data logger was a Pico DrDAQ (limits accuracy).
- Graph drawn using GnuPlot.
- 1.2V NiMH give working volts as good as 1.5V Alkalines.
- Unexpectedly, 750 mAh NiMH lasts twice as long as the 600 mAh.
- The Duracell Ultra M3 is only about 12% better than the Plus.
- NiMH pairs fail at different times, hence double knee graph.