Garmin Fenix 3 is a GPS watch, but has the concept of "indoor" (non-GPS) workouts. It will display power from ANT+ meters, including in a one-field data page. Some people mount theirs on the handlebars for visibility.

Independent testing put the battery at 5.5 weeks in watch mode. (20 hours to a charge in GPS mode.)

I can't tell you how long the battery would last as an indoor bike computer, exactly, but it should be in the dozens of hours.

Charging from empty to full takes about 2 hours.

Because the Fenix 5 has been around for most of a year (it's much less frugal with the battery) you can get a used F3 for not a lot of money.