The separate start battery is more for "start insurance" apart from the house bank,
but you know that.
The main bank can be drained by leaving lights or pumps on or may have suffered an
internal short and discharge. My house bank was zero volt recently when a near-hit
lightning strike wiped out a lot of electronics. A shorted diode drained the batteries
via the wind generator windings. Having the 2nd start battery saved the day.
Besides, as banks go these days, they often are bank-rupt and cor-rupt to their
worthless cores. Just saying.
More interestingly to me was the very brief but quite heavy current draw, which may actually
have been much higher than the Xantrex indicated. ( Being digital it will tend to average and
fudge a bit, unlike what a surge-responsive or peak-reading meter will show )
Another point, if battery connections are resistive or are poor, there is no way that current
can flow freely, a fact that is often overlooked by the electronically challenged. They'll measure
the voltage and say "ah, all's OK" but it really isn't as far as the VOLUME of electrons that can
run during starting is concerned. A little terminal twist and wiggle is often all that's needed to
get a decent crank instead of just a click (or not even!) from the starter relay.
Gads, why am I posting all this? Off to the hills till next week.