Battery tracker is a new plugin that seems pretty useful. Gives a chart of tracked battery levels, but more importantly it tracks the average power draw of the different games you run.

Some games draw wildly different amounts of power depending on area/etc, so getting average numbers for your total play session will be really useful for getting real battery use numbers.

To install, you need to first have decky loader installed, and you should find it in the decky store. You don't need to be in the testing branch of the store or anything, just the normal channel.