I got tired of paying $45.00 and more for power wheel batteries. I have a lot of grand kids and they love the motorcycles and jeeps I have. I took a 12 volt power wheels battery a part and found it was just two 6 volt SLA batteries. SLA is sealed lead acid . You can buy a 12 volt rechargable for SLAs under $15.00 on e-bay. You then can recharge them with a normal 12 volt battery charger and these things last! I am still using some that were removed from a security system that was installed three years ago.
If your power wheels vehicle has two wires from the batterty you are all set. Clip the plug off leaving enough wire in case you want to re wire it. Put on two aligator clips, red and black,  and you are all set.
I do not have the info for the 4 wire assembly.

Final note, avoid the SLA batteries that are rated under 9 AH Try as I did to get the ones that are 12 AH and higher.

On e-bay type in SLA