850 Remote door lock control batteries - lifetime?

How long do the two batteries CR1220 in the original remote door lock control of
your 850 Volvos last? I replaced a pair maybe two months ago with two cheap
pieces and though in my opinion I do not use them heavily, they are empty again.
Now I have paid a little fortune for two VARTA batteries and expect them to last
longer. Since friends with other newer cars tell me they have their remote
control batteries for much longer time I wonder how long the batteries last in
these gadgets.
Viktor

 

I owned my 850 T5 from Dec 95 until Nov 2001 and I never changed the
remote control's battery. I used the the car almost dayily.

Joerg

 

My '95 850 (owned since new) has 155,000 km on it. I use the remote to
open it every time. I've never changed the remote batteries.

Java

 

That is what I suspected! I usually have quite a bunch of keys in my pocket with
the remote control and the pushbutton is moving at very gentle pressure so
either the pushbutton is kept activated involuntarily often or there is a
problem inside the remote control. I will start using the second unit and see
whether it lasts longer.
Viktor