If I buy a HS2 with just 1 battery, can I use a 52V battery from another Juiced bike as the 2nd battery?

Well, yes and no, you can use the 13.0 Ah pack with the 19.2Ah pack, however you cannot use the 13Ah pack alone; it won’t fully support the high current draw of the HyperScrambler 2. We recommend you use 2 x 19.2Ah battery packs for optimum performance. You can’t use any 48V batteries, or any non-Juiced Bikes batteries, on the HyperScrambler 2.