Two large carbon fibre batteries in my workshop are used to provide standby AC and DC lighting for the house. The Elecsol 270 AH 12 volt is a carbon fibre type from 12voltz.com and weighs 62 kg and measures 51 x 27 x 24 cms. It is designed for marine and leisure use and can survive many deep charge/discharge cycles, unlike a car battery.
The battery provides emergency 12v DC lighting and also 230 volt AC lighting via a 450 watt sine wave 12 volt inverter. The inverter normally feeds part of the downstairs AC lighting circuit via a changeover relay.
We have several 12 volt fluorescent lamps around the house for those nights when Suffolk has no power! The system can also supply most of the downstairs 230 volt mains lighting circuit using the TBS Powersine 12/450 sine wave 450 watt invertor. The invertor has a 13 A mains socket outlet which can also feed other mains appliances as required. Check eBay auctions for a mains inverter
I have only recently added the second battery, so we should now have several days storage capacity for lighting and office use, in the event of power cuts. I have also been investigating 12 volt lighting to find something that is really bright. This eBay trader in Germany has just the thing. A 12 volt energy saving fluorescent bulb with a built-in inverter, brilliant!