Can boat batteries shock you? The answer is yes and I can in an empirical way say this is the truth. The way you can test this is on a stinking hot humid day in Florida whilst in the bowels of the boat sweating like a pig have your wet arm come in contact with the positive and negative battery terminals. Will this kill you? No! Will the shock hurt you? Not really. But in a cramped and confined hot space can it startle you causing your head to jerk up smacking the underside of the deck and let the wrench in your hand at the same time bridge the terminals causing notable arcy sparky stuff to briefly happen? Yep I know from personal experience this is very possible, and if there was hydrogen sulfide gas leaking from the batteries at the same time there might be a kaboom.
BTW the legal department on the fourth floor reminds me to tell everyone to not try to invent or test ways to have large batteries shock you. If you're going to try this anyway at least make sure you video it and use the revenue to help pay the medical bills. Although the voltage is low the amount of the stored energy is large and the law of unintended circumstances can raise it's ugly head.
To be honest I don't like to deal with batteries at all. They're heavy, bulky, almost always in awkward and at times nearly inaccessible locations.
In this particular case the charger in a new boat has failed and needs to be repaired, ahem, replaced. I think it never worked in the first place. This was made worse because it was one of the first devices connected to the batteries and the wiring was tie wrapped to large battery cables laying in between the battery boxes. But I have a flexible tool that takes some sting out of doing this job and it makes it safer.
These fleece blankets cost about $5 everywhere. If you don't want to make the investment then on your next flight you can whine at the flight attendant you're cold, and they will give you one. It's a cheaper version of the $5 one at Wallymart. I just stole mine from the Greyhound girl's big basket of winter blankets. I chose the safety orange colored one.
The blanket is folded in half twice (4 layers) and it makes laying on top of the front batteries to get to the back batteries much more comfortable. All these pointy things aren't poking as badly into me. Fold it twice more and you have a good knee pad.
Even better when you're in a cramped place you can safely set your tools on it. In my case there is a bulkhead on each side of me and I would have to keep the tools behind me making them a P in the A to get at.
Since this is kinda a sorta safety first thing here I have some additional advice on dealing with batteries.
1. Turn off all the batteries switches first.
2. Use a tie wrap to bundle all of a terminal's leads together. This stops a critical wire from falling into the cracks and being overlooked when you reinstall them.
3. Remove the negative terminal wires first, and then the positive wires.
4. Since the wires are off this is a good time to check water levels if need be, the date on the battery, and clean any corroded terminals and connectors. This is also the time to take a pic of the battery label so when it inevitably fails you know exactly what type and brand it is. You might as well check any fuses too. It would be comforting to know if the automatic bilge pump fuses are still good.
5. If you're replacing old batteries have some rubber gloves and rags to clean up any spills and to protect you hands from the nasty stuff that's in batteries. Wipe out the inside of the battery cases at the same time.
6. Reattach wiring starting with the positive terminal first. Make sure the nuts are good and tight.
7. If possible do this on nice cool fall day. August in Florida wasn't the optimum day.