You will bottleneck those motors with any NiMH pack I know of that you can get in weight. We bought two 18v custom packs for Tormenta 2, (4 drill motors) and put them in parallel, to get an estimated 60a-70a peak amp draw available from them. That figure would drive your motors and not starve them too badly, but the batteries will suffer a fair bit. And they were heavy.

I'd go LiPo. They're a bit intimidating at first, but smart enough chargers will stop before doing any damage if the setup is wrong, and once you suss it they're like any other battery technology. Difference is they weigh nothing and have incredible power figures.

Also, in truth, you'd pay a lot more for NiMH packs anything like close enough to the figures you'd need, than you would for a suitable LiPo pack.

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Two of those motors should get a machine moving around nicely.