Thanks for the responses, guys.
Yep, with multiple house banks there shouldn't be any need to require a dedicated starter, but when traveling to remote
locations it's reassuring to have a backup. Deploying a dedicated starter battery is probably a little bit of overkill though in this case, and I was concerned about mixing AGM
(house) and FLA (starter) chemistries.
And that's why I think the idea of the lithium jump starter has some merit. It provides an emergency
power source and they generally have USB and 12 volt outlets (and even lights) included which can make them handy for plenty of other things - for example powering a fish
finder on the dinghy
phones when on shore and even last ditch emergency use. I can't see any difficulty in creating a circuit that allows the unit to be quickly connected and disconnected for engine starting or portable use.
Having said that, some of these things seem to have pretty woeful connectors and jumper wires which would concern me. I'm also wondering what their track record
is like when it comes to spontaneously bursting into flames if they short out or otherwise fail?