I know you are not directing this at me, but ...

First, I assume you're talking about NiMH.

They have less energy per gram.

The voltage drop curve is very sharp, so you often don't get a warning before they drop way down.

They prefer to be discharged fully before charging, otherwise, you get less capacity, because of memory effect. LiIon batteries have little or no memory. If your usage pattern doesn't match a full discharge, you might get a lot less usage out of a NiMH battery. With LiIon, just charge it whenever you want, even if it's mostly charged.

I've read on this forum that capacity goes down in low temperatures.