I measured the battery drain on my unit. Looks like it's not going to be a nuisance after all.
I measured 12 ua @ 3V0 and 13 ua @ 3V6. Not impressive by today's standards, but within spec. The battery is powering two HM6116LP-4 CMOS rams. Maximum drain for them is 30 ua each @ 3V0 in standby mode. Therefore, a 650 mah battery should last for over 6 years. Wavetek's 'typical 1 - 2 years' is based on the maximum drain of 30 ua each.
So the dead Tadiran TL2150 cell in my unit (1/2AA rated for 1 ah) would have lasted for over 9 years!
By the way, it looks like the models 270, 271, and 278 are all variations on a theme. Start with the 270 and add more features for the 271 and even more for the 278. I didn't find a manual for the 271, but there are manuals for the 270 and 278 available online.
Ed