I got mine off the shelf at the Bulb+Battery near the track at GoPro for $45. Sales guy said all the karters get them there. Worked all season – 5 F-Series weekends — with a Leopard no problem.  I don’t know the model or name but was their private label brand.

Any good 12v 9Ah should do. Same as an X-30. A word of caution. Bought a couple of inexpensive 12v batteries from a battery store back when we ran a leopard. They last maybe a weekend of road racing. Discovered that those types of batteries do well in an emergency exit signs. They don’t hold up the vibration of a race vehicle. We may have been the exception to the rule as others did ok with cheaper batteries. I went to a large kart retailer and bought his best battery. The battery was as good as ever when the engine sold a couple of years later.
Our KA came with a Duracell 12v 9Ah but haven’t had the opportunity to used it yet. Too blinking cold out.

I’m thinking I might try the charger from Fastech when I get a lithium for my Ka.

http://www.fastech-racing.com/battery-tender-800-acid-lithium-junior-battery-charger.html

The battery/charger combo looks like a good deal. Plus I like that it is made specifically for powersports.

Anyone know if you can run some Automotive style LED 12v lights off the system without taxing it? We like to throw some on the kart for  night racing!