Can you build your own uninterruptible power supply with a car battery, an inverter, and a battery charger?
Can you hook the charger to the car battery terminals and then attach an inverter to the same terminals (in parallel they call it?). You then plug your computer or whatever to the inverter.
The whole setup would have to automatic. For instance, the charger can sense when the battery is fully charged and turn itself off automatically. With the setup, you shouldn't have to plug or unplug things manually based on what you're doing. It should be automatic, transparent, and operate in the background like any UPS.
Is this at all possible, or is it much more complex to get something like this working? Is this a fire or electrocution hazard? Will the equipment burn out the moment you hook everything together?