yeah, piccolo cant regenrate health (according to DBZ) only senzu beans can, He can restore limbs but thats irrevelant as body parts cant be severed in ESF. Except trunks sword of course, but then your already dead.
Same goes with cell.
But one thing i find that conflicts with DBZ. And thats buu.
He never charges ki, he always regenerates to 100hp after an attack (Unless he is killed), Only uses turbo rarely.
I rekon Buu should have unlimited ki, just change how much he can use at one time. He was always able to create blasts of various sizes in similar time periods.
Infact he was the "Perfect fighting machine" except for one thing.
He was too arrogant
(Goku always gets em on this one
)