Wish I got 13hours.
It depends on your screen settings. Mine is now approaching 4 years old and the life is dropping off. Battery replacement by Garmin is very expensive though so I’m persevering as it works for the vast majority of my rides/
On the map screen with the light at 75% I get about 6 hours. When I drop it right down to 1 or 2 bars I get about 8-9 hours. I can get about 12 hours (1-2 bars) if I am on a simple data screen.
IF you want longer rides or reassurance then it runs fine when plugged into a USB battery. I’ve done this numerous times when having a map was essential or the ride was very long. I now use and Anker battery mounted under the stem using one of those cheap Velcro torch mounts. I run it off external battery first as I was told this is more reliable.
http://www.amazon.co.uk/Ultra-Compact-Lipstick-Sized-Portable-External-Technology/dp/B005QI1A8C/ref=sr_1_2?ie=UTF8&qid=1430379321&sr=8-2&keywords=anker
I’ve never run out of battery like this and have had it on medium brightness for 15h.