GPSrChive Discussion Forum

To add a word of warning:

I once did extensive tests with a Garmin 276cx (a device which has really made me angry for various reasons). The results boiled down to the following: The Li-Ion battery from Garmin performed extremely bad. It reached only about somewhere between 60% and 70% of the capacity which could be expected from theory. I documented the test methods and the results (among others) in an article about the 276cx, and speculated about possible reasons for the discrepancy between theory and reality.

Once again, that article described the situation with the 276cx, and Garmin might have learned since. So please let me state explicitly that my findings might not be true for the Montana 700 series. I currently don't plan to repeat the tests and the analysis of the battery contacts for the Montana 700, so I can't say anything about it.

However, we still can learn from my findings that trying to predict runtimes of Li-Ion batteries from their theoretical capacities will eventually (I'd still say probably) lead to wrong results (and with wrong, I mean *really* wrong), just because they can be far away from their promised capacity (due to wrong charger design, sourcing inferior material at the spot market, and so on).

[ Side note: I didn't make such bad experiences with good NiMH batteries. Maybe cells which are rated 2800 mAh actually provide only 2700 mAh, but the deviations are negligible compared to those of Li-Ion batteries. ]

For those interested in the details, the article is here (you might want to skip to the section titled "Issue 6").

Best regards,

Themistokles

In addition, you cannot compare batteries on mAh alone. You must compare batteries using the power capacity or watt-hours. This assuming the devices have the requisite buck or boost circuitry to make the most of the power available, but that is a reasonable assumption, actually.

Thanks Peter for your comprehensive report about the 276Cx missing features. I strongly agree about the inability to charge the battery anywhere else but in the device. Same thing with the zumo motorbike models, the Alpha dog trackers and the Rino UHF radios.

I'm just setting a 276Cx up for a customer now and thought it may interest others that the USB method of charging a battery is very slow at around 0.1A (0.5W). This was tried using both the supplied and 3rd party AC/USB adapters. Mind you, the battery had 1% charge out of the box so maybe it would have increased in charge current later on in the process.

On the supplied AMPS Powered Mount and connected to a 12V battery (reading 13+ V) the charge current is around 0.3A (approx 3.9W).

KiwiGPS wrote: Tue Jan 18, 2022 10:39 pm ...the USB method of charging a battery is very slow at around 0.1A (0.5W).

Sorry but my statement above is wrong but too much time has passed to edit the post.

I have 8 276Cx batteries that are run down. Using the USB power meter I can see very flat batteries charging at around 0.85A (850mA). With the GPS on Diagnostic screen (Press Enter while powering on) the Vbat has risen from 2.56 to 3.65 Volts over 1.5 hours. When switched off then on and off (to bring up the normal charging screen with the battery percentage at the bottom) it is on 13%. I did the same last night and the battery rose from 1 to 100% overnight on the USB cable. I expect it will be 100% later in the day.

I could not find the correct Master Reset info for the 276cx - it is press and hold both the Page and Enter buttons while powering on. Release the Power when it switches on but continue to hold the Page and Enter 'till the "...erase user data?' question appears. The battery has progressed to 14% while writing this.