My 18.5 hp briggs and stratton won't turn over very easy. I've replaced batter, cables and starter. It starts to turn over but it's like it has too much compression. Any idea's?

Take out the plug and see if everything seems OK.

Most likely the valves need to be adjusted.

I did take the plug out and it cranked over like it should. Someone told me there might be a compression release valve that could be stuck. Is that possible?

Compression release just makes starting easier. At low speeds, there is little compression. At higher speeds there is lots of compression. If you turn the shaft in reverse slowly, there will be compression.

Too much compression usually means a valve adjustment.