Use them all the time.
What I'm really referring to is the cost of replacement batteries.
I mean, if the batteries stay the same how many times are you really replacing them? When you buy a new tool it (usually) comes with a battery. I've had a pair of Dewalt 1.5AH 20V batteries for... 8, 9 years? I've used them regularly at home and on side jobs, charging them 2-3x a gig sometimes since they charge in 20 minutes and I like that they're lightweight. Only now are they starting to not hold a charge and I have to replace them, they're at the point where after 2 or 3 1" holes through a 2x4 they slow down. But those two batteries are two of the 7 or 8 I have in total.