OK, I guess my assumption on your other post was incorrect, your boat is newer than I thought. I'm confused though by what you are refering to as the "battery box storage compartment", do you mean the cockpit seat locker? I'm confused because there is a lot more that I would expect to find there than just the battery box. There is another compartment in the O'DAY 23 cockpit, thet would be the built-in "ice box (just like on my DS II), but Although the one on the 23 is bigger than the one on my DS II, I hadn't heard of anyone moving the battery box into that compartment (though I must admit......if re-enforced a bit....it would work better to stow the battery there than use it to keep food and drinks cold!). If that is the compartment you are refering to ("cockpit ice-box") then see my reply to your other post about leaks, the bungee-cord "hinges" are what I would expect as your leak source. I've included a pic of the "ice-box" hatch on a DS II and a drawing of the 23 cockpit for reference.
Leaks could be caused by deck cracks, but those most likely would not really show up when the boat is just sitting. Cracks would need some kind of outside force to open enough to leak usually. I'd check around all deck fittings fro minside while someone focuses a water hose on each spot. Also, the cockpit drain may be leaking resulting on water in the bilge, for that you would need to crawl into the cockpit locker on the portside and shine a flashlight on the drain fittings, located under the aft end of the cockpit. If either fitting (cockpit end or transom end) it could allow water to leak in and could be a BIG problem if boat was in the water. There are several postings on this web site about fixing that cockpit drain. The same basic setup was used on the 23 (1977-85). the 222, and several others (maybe all O'DAYs 20-26 ft long). I have added 2 pics of the typical O'DAY cockpit drain (pics are from a 222, but 23 will be similar as far as I know)
