>>My golf cart batteries are 7 years old and dying after about 4,000 recharge cycles.

Really *golf cart* batteries? Or is that just shorthand for lead-acid? If they *are* actually lead-acid golfcart batteries, the lead is formulated to be resistant to vibration (typically with antimony) which shortens battery life (easier for 'dendrites' to form).

There are 'deep cycle' L/A batteries that are probably more appropriate for a boat.

That said, I was unaware of this battery tech. At a minimum, it can make launching deep space probes safer for us groundlings as (AFAIK) the ones using RTGs use plutonium - and I would NOT want to be downwind of a launch gone wrong.