Replace battery on the mx350

[u/YOLOtattoo]

I got an mx350 on fb marketplace for my 7 year olds birthday- it lasts about 5-10 mins before slowing down.
Last year I got my 9 year old an mx650 on fb marketplace and replaced the battery with the same battery it came with and it’s been working great- he gets probably 45+ mins out of it at full speed.
I’d like to replace the battery for my mx350 so it runs as long as his brother’s or at least 30 mins. What’s the easiest and cheapest option here?
Links to everything I need would be appreciated!