On board battery(ies) for powering radios/Flarm etc

Just a quick question.
Had a brainstorm the other day, might have hit my head, don't remember, who knows...

What are y'all using for on board power these days?

Last I flew, we were using 6? amp hour gel cells by Hobbico from Tower Hobbies. (The kind that powered the little Powerwheels Jeep your kid/grandkid rode in 20 years ago)

What kind of power capacity are folks using?

I was working my big a$$ Milwaukee 10" chop saw and saw how compact the 18v, 9 amp LiPo was, and how fast it charged on the included rapid charger and got to thinking 1, 2 or 3 of those on a semi-custom mount with built in voltage regulator would be right dandy in these birds, and available at the big orange box store if a replacement is needed in a hurry.

Just a thought. Please return to your regularly scheduled mayhem.