4.3l Mercruiser will not Start

[techmitch]

Thanks Everyone for the help. There are 3 batteries on the boat, I was under the impression they were used to start the engine(s) as it turns out 1 battery is used to start the starboard Engine and the other 2 are used to start the port engine. I switch the main cable from each battery and the Port engine (bad engine) attempted to start. Took the 2 batteries and had them bench tested - 9volts and could not charge - replaced the 2 of them. Hopefully the boats charging system is not bad. It is in a marina on shore power.
Thanks Again for all the help!!!!!

You guys are the best,
Jeff

Make sure your onboard charger is working properly AND not cooking your batteries.