EDIT: on hold while I check conditions
@Harper pointed to the fact that my battery is rated to draw 165A continuously for an hour, which should cover the needs of my inverter when my vacuum starts up. I do sometime have to switch over to a backup battery, and I need to verify this hasn't somehow interfered with the measurements. In the worst case, it might mean that the measurements were made using a 136Ah AGM battery from Sunwind with a rating of 67Ah with C=1 - about half that of the Concorde.
Still, the points on wire thickness might be relevant ... I usually employ really thick (35mm2 - 70mm2) jumper cable wires and the length between the inverter and battery is less than a metre, but in this case I have just relied on the cables supplied with the inverter, which are far from thick: maybe 2,5mm2.
I have a single 12V battery (a 305Ah Concorde Sun Xtender 2580L) feeding the power needs of my off-grid cabin. This has worked well, but I recently got a 2000W inverter which introduced a new problem: power surge and continuous high-power delivery.
I had figured out that my setup would be fine, since I only needed this inverter for ten minutes or so during a weekend (powering a 220V 1400 Watt vacuum cleaner), but this failed to work: as soon as the vacuum powers up, the shown voltage on the inverter drops from 12.3V to 9.3V. I take this as a sign that a single battery is unable to sustain such a high load. What I'd like to know is this:
How can I know how "big" a battery bank I need to sustain X Watts in continuous power draw? Is there some indication in the battery specs that will help me in finding the numbers, or are people just using some heuristic, like "max power of a battery bank is approx 2x its numeric rating in Ah"?
P.S. Feel free to talk to me in Volts, Ampere hours and Watts. I can do the math :)