The battery in my 'tuna lasts about two years. Toyota comes out and jumps you free during the warranty period. The battery itself is prorated.
If you are a B-Quik customer, they come out and jump and check the battery for free, and if you need a new battery, they'll deliver it free.
I just bought a new battery in November, and I bought this and will try using it every six months to see if I get more life, or in the event I wake up with a dead battery.