Green light always on and battery charge barely lasts a day

That might still be within reason. I tend to charge once a day pretty much.

Here the battery saving tips from Apple:

Batteries - Maximizing Performance - Apple

These two articles might give some ideas too:

https://buybackboss.com/apple-watch-battery-draining-fast/

https://www.businessinsider.com/why-does-my-apple-watch-die-so-fast

Daily charging is typical with Apple Watch.

Charge it while you sleep, same as charging the iPhone.

If you want longer with the Watch Series 5, select Theatre Mode; blank the display.

That’ll usually get closer to two days for a Series 5 cellular model.

From some testing, 83% charge remaining after 12 hours of light use, Series 5 display blanked.

I actually have to charge my Watch SE later in the evening and NOT overnight.

Watch fully charges in two hours, or so.

I sleep with my Watch for sleep tracking and as my primary wake alarm now with both sound ( wrist is always near my ear ) and set to heavy vibrations on my wrist.

Best case scenario for the battery is 18 hours. That's why I won't buy an Apple watch, even though I want one very much. Eighteen hours, meh.

FWIW, was at 71% remaining at ~18 hours last night, Series 5, light use, no cellular use, with the display theater’d for the day.