I'm using two CR2016 Lithium 3V batteries.
Batteries in mine are ok, it's just the "open" button on my key has a crack across it and the internals are a bit sqaushed.
27 presses of the button to operate, 21 of those presses stood right next to the car door - I won't be beaten by a bit of plastic and metal.
I've got remote central locking and I'm damn well going to use it