[E-Revonut]

I don't know that your charger could handle 24V input, you may want to look that up.

Charging a 12V 7Ah battery shouldn't take that long. That's about the same as a 3s 7000mah, so even if your charger is only capable of 50W that should still take less than 2 hours. However on the flip side it won't run your charger for long either, probably about 1 battery pack.

How are you getting to the park? If one of your friends is driving pop the hood and charge off the car battery. You can charge many packs before you need to worry about killing the car battery