Your correct on the power consumption of an invertor. They will draw from the "grid" later what you used during a power blackout plus about 10% to 20% in heat due to charging losses then plus a little to keep the batteries topped up which is less then keeping one light bulb on all the time after the batteries reach a full charge.
Actually the only reason i got a 2.5Kw invertor is to make sure i have enough surge capacity to run my fridge which it does easily otherwise it runs a fan, TV and computer and table lamp with power saving 12w bulb so i only have 4 Trojan T5 batteries just now. If I need any more power then i start the planta.
By the way a quick conversion to dollars works out to $998 for the invertor, cables and batteries and its a Dominican made unit but very well designed using modern QUASI switching MOSFET technology so its a lot lighter and more effecient then the older units.
I still be interested in a blackout report log though so we know whats happeining!