I'm a bit out of the loop with the latest dashcams, but maybe have a look at a Mobius Action Camera. I ran one as a dashcam in my car for most of the reasons above - I definitely didn't want something big with a screen on the back of it. Attached it to the solid 3M mount, tucked it up behind the rear view mirror and forgot about it most of the time. No silly light grey or chrome accents on it to make it obvious in the windscreen either. Time/date/speed can be removed using a program on a PC (with the camera connected via USB) and all other settings are adjusted this way as well, but you don't have to connect it to the program as it will work out of the box. Apparently the built-in battery lasts up to 2 hours although I never used it that way.
Downsides are it is only 1080p at 30fps or 720p at 60fps and I'm not sure if it conforms to your power requirements (or how well it would work on a bike), worth a look anyway. Night time footage is fine in built up areas, but where I am with barely any street lighting it isn't great. Mine ran flawlessly for 4/5 years and never skipped a beat until a year or so ago when the summer heat must have finally got to it and warped the plastic casing so it no longer slots in to the mount properly, but I'd take a guess that it would still record footage fine. Definitely worth a quick look as it instantly came to mind when reading your requirements, but I'm not sure how well/if it will work on a bike as it doesn't have image stabilisation so you'll want to check video quality, etc. as well.
A fair few YouTube videos make the footage look mediocre, but it could just be how people render the footage and YouTube in general as mine looked good when playing directly from the PC. I was pretty impressed for under £100 and to put it another way I've not been tempted to replace it because without spending £200+ the only camera I've come across with better video quality is the Viofo A119/129, but that is irrelevant.
Downsides are it is only 1080p at 30fps or 720p at 60fps and I'm not sure if it conforms to your power requirements (or how well it would work on a bike), worth a look anyway. Night time footage is fine in built up areas, but where I am with barely any street lighting it isn't great. Mine ran flawlessly for 4/5 years and never skipped a beat until a year or so ago when the summer heat must have finally got to it and warped the plastic casing so it no longer slots in to the mount properly, but I'd take a guess that it would still record footage fine. Definitely worth a quick look as it instantly came to mind when reading your requirements, but I'm not sure how well/if it will work on a bike as it doesn't have image stabilisation so you'll want to check video quality, etc. as well.
A fair few YouTube videos make the footage look mediocre, but it could just be how people render the footage and YouTube in general as mine looked good when playing directly from the PC. I was pretty impressed for under £100 and to put it another way I've not been tempted to replace it because without spending £200+ the only camera I've come across with better video quality is the Viofo A119/129, but that is irrelevant.
That's not to say the Viofo is bad as it is a pretty good cam.