Good Digital Multitester
Now that you've got a boat there are two choices: 1, learn to do the work yourself and save money, or 2, hire it done. If you want to be self sufficient and do it yourself one of the best tools to get is a good, accurate multitester. A good brand to get is a Fluke. Don't worry too much about the price because it'll pay you back many times over. Use it to see what flashlight batteries are good. Check the camera batteries, watch battery, etc. Troubleshoot the electrical circuits. Check if you boat or the neighbors is hot. There are millions of uses.With a multitester you can check the voltage on each battery and see what's hapening with those electrons. Check Products/Digital Multitesters in the link below. Get something that measures at least resistance and voltage as a minimum.