Power bank charging

It should be able to work/charge off of power bank. You might need to try a power only cable instead of power/data cable.

I've used various power banks in the past without issue.

Yeah.  I've charged mine off a variety of chargers and power banks no problem.  I know of no setting on the device pertaining to charging.  If it's on and then plugged into a power source, a banner across the top says "Charging" for a few seconds.  Unplug it and it says something like "Power lost" across the top for a few seconds.  If it's off and then plugged in, the charging screen shows while it's charging.  When disconnected from the power source, it automatically boots up.

Yes I've tried a couple of power only cables but still nothing. 

ive just tried mine on a couple of different cables & it charges ok. i use the genuine garmin  power lead on the bike as i strap a little duracell battery on the stem. the battery only lasts 3.5 hours before wanting to go into power save mode without but i do have a lot of extras added on.

It's a weird one, thanks for the responses 

ive been caught out like that a couple of times, charged my 810 and failed to turn it off when removed from charger, battery dead when come to use 

My 820's battery is getting bad.  I rigged up a small roughly cylindrical power bank on my bikes to connect to the 820.  I'm using an "Aibocn Power Bank 6700mAh Lipstick-Sized Portable Charger" (~$13) and a "StarTech.com 3 ft / 91cm Micro USB Cable - A to Left Angle Micro B" (~$5) I got at Amazon.  The power bank has ~10x the nominal capacity of the 820s battery so is plenty.   The right angle uUSB cable exits to the left from the back of the 820.  I used some stick-on velcro and a velcro strap to fasten the power bank under the front of the bikes' top tubes.  The power bank is not waterproof and with the uUSB cable connected, the port cover on the back of the 820 is open, so this would be NG in wet conditions.  I'm considering getting a new computer but am gun-shy on getting a 530 or 830...

Pretty common. The batteries they use aren't the best quality and they're tiny. You can buy a replacement battery and rear housing on ebay probably for about $20.

I eventually gave up and bought a 530, the difference is incredible, I only charge it every 200 miles or so and normally have it in nav mode.

I'd definitely recommend it.