@babyjigs 3 checks I would definitely do are:
Connect to it with the app and see what battery percentage it's currently at. Anything between 40% and 60% is likely fine but not a guarantee. If it's fully charged or empty I'd be a little concerned that it's toast.
Next check is see if you can connect it to the OWCE app and see if the cells are within 0.1-0.2 volts of each other. Anything else might indicate a bad cell.
If you're able to take it for a test spin that would be good but won't tell you much other than it at least works.
It might be worth asking when he last used it and what percentage he left it at. Being an RC enthusiast he probably left it at a good level but worth checking as I've had batteries from "enthusiasts" that left the things at full for months 💀