What happens if you don't pay your taxes quarterly?

Being self-employed for the last year, I've been paying my taxes quarterly bc that's what my CPA wants. I don't really meet with my CPA but once every few weeks just to give him my check stubs so I don't want to bug him with a phone call over a silly question like this but what happens if I decide to stop making these quarterly payments and pay all at once?

I invest alot in cars that i buy at auctions and fix in our shops and the extra cash would definitely allow me to generate a pretty high return with me keeping all those payments and investing them in some vehicles today.

Is the penalty a flat fee? or is the penalty a percentage of income?