Mitch,
I've only seen two 1986 O'Day 222s up close, mine and my friend David's which he bought from my friend Walter years ago. I'm pretty sure that David's boat is set up similar to mine with the battery on the sole plate in the cabin. In fact I had emailed him about this and he replied that his boat is set up exactly like mine as far as the battery placement behind the step in the cabin, under the cockpit is concerned.
I don't doubt that one or two of the O'Day factories built their 222s with a provision for the battery in the lazarette. They were always experimenting on these boats trying to find ways to cut costs.
When you think about it, it's a heck of a lot cheaper to relocate the battery storage area to an existing spot in the cabin where they only needed a battery strap and plastic brackets than it was to glass in a special mount for the battery inside the Port lazerette. It's possible that when they mounted the battery in the Port lazarette, they figured it would offset the weight of an 8 hp outboard motor on the Starboard side of the boat's stern. The best trade off I can see is more room in my boat's lazarette and I still have plenty of room to store gear next to my battery box on the sole plate.