a 52V 50AH battery is like 2600 watt*hours, thats massively huge and heavy.

if your motor is overheating, get into the controller settings menu, and limit the maximum power to like half what the motors rating is, and plan on a little more pedalling and less pure throttle.

me, I'm using a mid drive Shimano now... at its highest pedal assist setting it can still go 60 miles on a 500WH battery, thats 1/4 the size of what you were talking about, but because its pedal assist, you will be pedaling the whole time.

if you're riding with a group thats going too far and too fast for you, find another group. more you ride at a comfortable pace, the stronger you will get and the better your endurance will be. use your gearing so your pedaling is smooth and at a reasonable cadence, at least 60 full pedal turns per minute, and that will build your endurance.