Make sure to distinguish between amps & amp-hours (also watts & watt-hours).
Amps used per day is a nonsense term. So when you say you came up with 347 amps per day it makes no sense (I have a pretty good idea of what you mean but it confuses the discussion)
Amps and watts are an instantaneous measurement. Your truck engine may take 600amps @ 12v to turn over but since it only takes a few seconds to start, it uses almost no amp-hours.
On the other hand your TV may only draw 4amps @ 12v but if it's on for 10hours, it will burn thru 40 amp-hours.
Second, issue is your laptop has two separate things going on.
- Your average laptop will draw somewhere around 60-70watts when running.
- The battery charger may or may not charge at the same time or the same rate as it's feeding the battery...ie: if you shut down the computer and the battery isn't full, the charger will keep charging.
- Then you have parasitic losses. If the battery is full, don't leave it plugged in as keeping the brick powered can eat up 5-15watts. Not a big issue when plugged into shore power but when operating on the RV's battery bank, it adds to the amp-hour consumption.
- In the end, I would find the wattage draw of the computer and add 20%, then multiply by the assumed hours per day to get an estimate of the watt-hours per day. Divide by 12 to get an idea of the amp-hours.
