One of three 13.2V modules.
The loss in capacity is somewhat overstated since lead acid batteries are rated at fractional C rates, while the lithium ion batteries are rated at 1C. They also came with balancing boards, but they don't even fit on the cells. (The drain FETs don't clear the vent caps without additional washers to space them out vertically from the terminals.) Not worth the extra $100. Get yourself one of these instead for $13. They don't balance the cells for you, but they do have an audible alarm for over and under voltage, so you know to stop driving or stop charging and balance if necessary.
I was a little worried about the power-handling capability of these cells, since they are only rated for 3C continuous discharge (120A). The kart at full tilt sends 300A to the motor. I wasn't expecting 300A from the cells (except at high speeds, the motor current is higher than the battery current), but something around 5C or higher for peak discharge would be nice. The internet is fairly bad at documenting the capability of these cells. The closest thing to consensus I found was a per-cell resistance of about 3.5mΩ. Assuming a low-voltage cutoff of 2.5V and an open-circuit voltage of 3.3V, that gives a peak current of (3.3V-2.5V)/0.0035Ω = 229A, and a peak power of 2.5V*229A = 573W. With 12 cells, that's almost 7kW, which would be just about right for the kart.
Enough math. Here's some on-kart test data:
This is for the full 12S battery pack and includes the resistance of the bus bars, fuse, wiring, manual switch, and contactor. It's at about 75% SOC and shows both charge (regen) and discharge data. The output is very linear, which I guess makes sense for a cell with relative high DC resistance. The resistance per cell came out to about 3mΩ and it has no trouble putting out 6kW, with still a bit of room before the low voltage cutoff (30V for a 12S pack). In other words, works as advertised by the internet or slightly better. For the price, hard to beat these cells. But don't expect to win a drag race against A123s.
If nothing explodes, there should be new kart test drive video soon!