Flooding batteries:
It's bad for all batteries, worse for good NiMh, and even worse for good Li-on. It's a direct correlation with how bad the flood is, and how good the battery is at delivering current. Saltwater shorts them, electrolysis starts, contacts start dissolving, and gas builds up.
Rechargeables have lower internal resistance, which allows them to deliver current better. That's good for the electronics most of the time but very bad in a flood as the chemical-electrolysis reaction is worse.
First thing you should do is get the batteries out, and rinse the cavity with fresh water.
10,000mA batteries.....yes, that would be good but don't hold your breath. They keep making electronics smaller and something has to give, often the battery. It's easy to change out above water, not diving. Frankly one of the better ideas was the old 4xAA Canons. Good size to hold, batteries lasted a long time, plus easy and cheap to buy. Didn't fit in your pocket though.