"David Lesher" wrote in message
news
Gunner Asch writes:

I'm guessing 12 inches to the power of 3 - or 12 cubic
inches - - -

An approximate size of what will fix into the locker....

Into the locker? For transportation only..right?
Absolutely.

Best not be running your genset from inside the locker......

Hardly. If we were underway, the iron genny would be charging
both sets of batteries. But when you show up at the mooring and
the bilge pump has run the house battery string down, and the
Volvo would not crank fast enough to start..... then what?
...

Bring a freshly charged lightweight Lithium jump starter pack?

Lithiums are expensive for their Amp-hour capacity but they are small,
light and well packaged to bounce around in a vehicle. The power
terminals on my Whistler Mighty are recessed behind a snap-shut rubber
flap. It comes with a rugged zippered nylon case to protect the
battery, cables and chargers.

Better rated:
https://no.co/products/power/jumpstarters

Perhaps you should look into why the solar panels didn't charge the
starting battery.

Older batteries may require higher charging voltage. My testing
indicates that they come back to normal if topped up periodically,
like monthly, though some of mine have degraded in two weeks and
needed 15V or more to restore them, which the usual charger won't
provide. That's why I built my own metered adjustable grid / solar
charging controllers and prefer batteries with caps to check and top
up the electrolyte.

I don't (yet) have a good plan to obtain long life from unattended
outdoor batteries. I have to set the charger voltage and current to
match their condition. My industrial experience was all with systems
the users maintain, like telephone exchanges, portable medical devices
and the Segway.

Recently two of my 12V 7A-h AGMs failed with a bad cell. The only
symptom while charging is the current doesn't decrease below 1% of the
A-h capacity in a few hours, otherwise the charging voltage appears
normal, but they drop below 11V when briefly loaded.

There are computerized chargers that test battery condition although I
think I can do more with lab test equipment including a carbon pile
load tester. An automatic charger that included one would be dangerous
if it malfunctioned.
-jsw