[Marvin]

I need a couple of 3S Lipos for a 1/8 Buggy conversion. I'm going to run them in series, for 6S, and have calculated that I need ~5400mAh at that voltage to get the run-time I'm after. I also need them to be as light as possible, as that much battery is always going to be heavy.

The two Lipos I have found that fit these criteria are:
Trakpower 5400mAh 3S
ThunderPower 5400mAh 3S

The Trakpower only has a 16C continuous discharge rating, which using BrianG's power output calculator, appears to be just about enough (using previous data, 18.5V, 6600mAh, 20.5 minutes, then changed to 22.2, 5400mAh, 20.5 minutes). However, it can be charged at 2C, and, as a racer, that's good news. Also, I can get these easily in the UK, and are cheaper when I get my LHS staff discount.

The Thunderpower has a much better discharge rating (20C), but can't be charged at 2C.

Which would you pick? Or is there a better alternative?

I would also consider a single 6S lipo of the same capacity, or two 6S lipos to run in parallel, but I haven't found any that fit the capacity I'm after, not at a lightish weight anyway. (I'm looking for less than 850g for the batteries really).

I know this is kind of picky, but I like to get things right.