Sorry to hear about the ESC. I think it's just undersized for a 3S LiPo. Awesome that you got a whole new boat. I plan on getting some more back up ESCs for when I take the boats with me on vacation.
I have a Hyperion EOS0606i AC/DC charger. It works well. It balance charges, discharges, and has a store mode that is handy. You may know this, but you want to store your LiPo batteries around 60%. I then try to cycle them about once a month if I haven't used them. Now that I have more RC toys I am looking at getting a multi-charger that can do 2 or even 4 batteries at once. I found Lipos confusing at first and did a lot of reading to figure out what all the numbers mean. I suggest you do the same if you aren't sure. Things to look for in a charger are the wattage rating. The high the wattage, the better suited it is to handle bigger batteries. Does it come with a built in power supply ,AC ? A lot of them are DC only and require an additional power supply. Most AC/DC chargers are lower wattage but fine if you are charging smaller batteries. By "Smaller" I mean lower Mah ratings and/or cells. So for the boat batteries, a 50w charger is fine. If you get into bigger boats or trucks/cars then you may want a more powerful charger. I saw the Hyperion EOS0606i up for auction on eBay today. They usually go for $60-$75 used.