Things to know:
The Peanut's light has a 25-minute run time at the highest setting. Find that assassin quickly!
The battery takes 35-55 minutes to recharge.
The battery itself is a 10180 Lithium Cell 70mAh. A pack of four sells for around $13.00 on Ali Baba, though I'd look elsewhere.
My point: the battery seems easy to replace.