Does anyone have any recommendations for a robustish external battery to make my Garmin last a bit longer (it’ll only last 7 hours)?

Most seem bulky or with a load of wires hanging of ’em, ideally something that’ll strap under the stem in a fairly inconspicuous manner. Water resistance is going to be limited as it’ll have wires coming out of it up to the computer but I want something that can deal with normal Cumbria weather!

I would buy a 18650 single cell phone charger and set about waterproofing it myself. You could possibly plug a short mini usb lead into it then tightly wrap some electrical tape around it.?

What could possibly go wrong.

£3.50 down the drain when it gets wet.?

What if the Garmin gets wet?

I thought the battery on these should last 20 hours. Any idea why it’s only getting 7? Worth checking with Garmin on warranty?

Try turing off things like Ant, WiFi and GPS and you might get closer to the max advertised battery life. Completely defeats the point of having it but anyway.
Garmin do sell an external battery pack thing but its about £70.

Cheers, Internet didn’t really help so I just went to Maplins and bought an AA ish sized one, fits nicely under the stem. I’ll just try and bodge a bit of waterproofing as per Neilson’s idea around the USB points on the Garmin/battery and see how it goes, I’ll not need it that often but have in mind some longer rides when I’m off work.

Garmin are very optimistic with the battery life, as above I’d have to knock everything off and put the screen to its darkest setting to get close to 20 hours, I still don’t think it’d get past 15.

Seen the Garmin one, it’s just a re-badged powermonkey, doubt (really hope!!) I’ll be needing the solar panel!