I've found Energizer Ultimate Lithium's are fantastic after years of rechargeable batteries not lasting long enough, even when the GPS has been changes to suit them

Blog here http://johnclimber.com/2015/02/14/when-will-you-die/

What are your favourite batteries for your GPS?

What setting do you have on the gps as that makes a massive difference?

You can change most gps units for use with several different types of batteries to get the most out of them

If I'm doing something like the bb200, or like Rovaniemi next week, I'll splash out on Lithiums. If it's any ride where stopping for a minute or two won't hurt then I'll use rechargeable batteries.

I always use rechargeables. They're cheap and re-usable. I get 14-15hrs out of a set, even in cold weather. The 7dayshop ones have been fine. I was using Ansmann before that.

Well they finally died today, 32 miles in so 525 miles on a set at £2.50 for two

When @ home, I use Duracell rechargeable in the Etrex20. I might get 10-12hrs runtime in the Garmin like this.
When out in the field for anything longer than 3 days, I'll use Energizer Lithiums (and carry a spare set). I get good lifespan from 'em with the Garmin set to 5 second backlight (approx. 60hrs run time).

Greetz

S.