I seem to get about 4 years from a pack. I had a 3500, 4200, 5000 go bad in the last year here but the lower #'s were the oldest.
Venom has a program where you can get warranty on them. 1st year is replacement, 2nd year is % off and 3rd year and on is 30% off a new battery.
I cashed in on that and got them off the venom group website (
http://www.atomikrc.com/). that way there is a receipt right there. lipos you can register on their site to. orders over 60$ i believe were free shipping (even to canada except duty/tax fedex)
I did have to cut one of the wires on the battery, take a photo and send it in to get the deal