My old Soligor spotmeter takes mercury cells, but I invested in a couple of C.R.I.S. adapters for silver oxide cells. This is a pricey solution - four of these little things would buy you a used Pentax spotmeter - but I have some other equipment that can share them.
Performance seems to be on a par with the original batteries. I rarely use it for low light work which is where any non-linearities would really show.