[TenTec] snaphat expiration date? battery longevity?

[denton sprague <denton@oregontrail.net>]

how does one tell the date of manufacture/expiration date on a snaphat memory 
batter for a ten tec orion? 

I finally located a 1.8 kHz crystal filter for my Orion 2 and since had the 
cover off, decided to replace the yellow memory battery, but previous owner has 
already did that!

Numbers on the existing battery and the new ones I ordered are the same