Well I was finally able to put my battery system to the full test on Sat night
Operating all night from 5pm to 5am off the
two 150 ahr batteries were:
Running from 1000W inverter:
White light in shed and dome (on when needed)
Laptop
NJP mount (mostly sidereal tracking with a few GOTO's)
CCD camera (running at -20C)
Guide camera
Atlas focuser
SX USB flterwheel
Two dew heaters on the AG12 (OTA and secondary)
3 X AG12 rear cooling fans
Charging mates Canon camera battery (twice)
Charging my I Phone (once)
Running direct from the 12V batteries:
12" Skywatcher dob GOTO mount, regularly in use (lots of GOTO's)
Two dew heater straps on the 12" dob (12" around OTA and 4" around eyepiece)
A 12V hairdryer to clear dew form my mates 6" SCT and camera lenses and my dob secondary, so getting down to -3C and dewy it was working pretty regularly throughout the night.
At the end of the night even in that cold (when batteries struggle more) and when the load was removed the batteries still read 12.3V or about 50% charged.
So this was my expectation when deciding on the size of system to install and I am happy now that I will never run out of power under normal conditions
Mike
...t'is not finished yet but I am very happy with how the observatory has come together and everything works (touch wood), it's comfortable and already had a few kips on the sofa lounge, has great panoramic views to sit under sipping coffee in the wee hours and once the new 12" goto dob for visual use is commissioned this weekend..?.. I recon I will truly be in heaven 
) and Angie will never see me....
