Hey, if it rolls or flies it fits in the vehicles section

So my family is trying to strong-arm me into buying a replacement Fisher-Price battery for a Power Wheels electric car/jeep thing. The problems here are many. They're just assuming the battery is the cause of their problems, the battery looks brand new and is supposed to last 15 years, they don't actually know what they're doing, they don't take proper care of anything, and they want me to replace the $30 battery.
I don't know jack about electrical stuff, so I come to you guys. Without having two Power Wheels cars, two batteries, and two chargers is there a way to conveniently test this battery to see if that's what actually needs replacing? Are there cheaper alternatives to the Fisher-Price battery or is this one of those things you're better off buying the real deal on? On the flip side is there a BETTER or stronger battery that will improve the performance and is worth the cost?