When you talk of the "Motor battery" being 750 amps, you are refering to cranking amps...
However what we are concerned with in HOUSE batteries is amp hours..
750 cranking amps would be about a Group 27 which is typically about 100 amp hours.
But wait there is more: That is a STARTING BATTERY, good for high current short term (like 30 seconds tops) Loads but not so good for "The long haul".
The most popular RV battery is a Golf Car battery,, GC-2, used in pairs (Since they are six volt packages) in series... This gives you 230 amp hours give or take depending on the exact model you buy, and whats more they are DEEP CYCLE batteries. Designed to provide a greater percentage of their total charge but do it much more slowly.
NOTE: All Amp hour ratings in this post are C/20 (Capacity over 20 hours) rate. Some battery companies use different capacity rating systems so as to give a higher number.. They lie.
And again there is more
A starting battery run down to below half full is quite likely a door stop, Good for trade in, and not much of anything else.
A DEEP CYCLE is designed to go to 50 percent state of charge and I ran my interstate U-2200's down well below that at least half a dozen times in their 9 years of service.. I now have DEKA G-20s (A GC-2 battery) So far have not tried to kill them.
DEEP CYCLE are way better at recovering from an "OH @**T!" discharge.
Marine/Deep cycle... is a starting battery.. Try to avoid it.
YOu can also get G-12 batteries now days (12 volt deep cycle golf car, about 120 amp hours as I recall but Ive not seen a chart on em recently)
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times