The extreme power consumption of a RaspberryPI 4 is about 7W [1]. The battery is 144Wh. If battery can discharge 100% that's about 20 hours and about 10 hours for 50% discharge. This all assumes the CPU is pegged at 100% and it's not an older model which consumes less power.
If you put any effort into power optimization you can get an r-pi under 2W at fairly high CPU load. r-pi like could also be one of the much more efficient single board computers that run under 1W
> Certainly would take a lot it seems to drain it to 0% before the sun came up.
It depends.
Different types of batteries have different recommended levels of discharge. Acid batteries should not be discharged more than 50%, while lithium batteries can be discharged up to 80-90%. The Blue Ion 2.0 lithium battery is the best one available, as it can be discharged up to 100%.
I guess it could be possible.
[1] - https://www.pidramble.com/wiki/benchmarks/power-consumption