Copied from another thread in case it's useful:
(No adapter needed)
The one I got from the local Batteries Plus store is white with these markings:
PC164 / TR164A
Also, the + end of the battery is flat, while the negative end has the bump; opposite of any other battery I have seen. So it's easy to put in backwards and think it doesn't work.
WARNING: The Batteries Plus website is entirely USELESS for finding this battery.
But, it looks like Zbattery has it here: http://www.zbattery.com/tr164a1.html