Capacitor to replace battery - help me with specs please
 

We bought a used kids mini dirt bike for cheap (poor guy had the fuel tank line running into the vent line and he was done with it not staying running - took me a while to find that after checking float level twice and jets etc) that comes with elec start, headlamp etc. Don't need elec start or the heavy battery that is mounted at almost seat level. It has a kickstarter so we plan on using that. Can't just rip it out but was reading that I can replace it with a Capacitor. Where do they sell them (types of stores as I'm in Canada) and what specs do I need?

I did a bit of research but I'm not comfortable yet.

The battery is a 12V 4Ah and has roughly 80 CCA, not that I'll need any CA's.