I also find that my 1KW can't keep voltage up if the car isn't running, though this may be due to the fact that I haven't got a great battery and my cables aren't that heavy duty. Suffice to say, I'd keep the engine idling if I was to run power tools off of it.
Another way to look at it is that most 12v batteries are about 100 amp hours, or 1200 W hours, an inverter is 85% (at worst) efficient, so you can get 1020 Watt hours out of the battery converted into AC before the batteries is completely dead. Since you're getting a 1000 W inverter, you could at max get an hour at full load, best case scenario. However, depending on the minimum voltage the inverter needs to run, you will probably fall short of an hour by quite a bit, since the voltage of the battery is going to drop below what the inverter needs before it's 100% discharged. Also, I wouldn't recommend this with a regular car battery, since this is more the type of Job a Deep-cycle is designed for. By repeatedly discharging and recharging a starting battery, you'll probably jack up the cells and have to replace it.
Another way to look at it is that most 12v batteries are about 100 amp hours, or 1200 W hours, an inverter is 85% (at worst) efficient, so you can get 1020 Watt hours out of the battery converted into AC before the batteries is completely dead. Since you're getting a 1000 W inverter, you could at max get an hour at full load, best case scenario. However, depending on the minimum voltage the inverter needs to run, you will probably fall short of an hour by quite a bit, since the voltage of the battery is going to drop below what the inverter needs before it's 100% discharged. Also, I wouldn't recommend this with a regular car battery, since this is more the type of Job a Deep-cycle is designed for. By repeatedly discharging and recharging a starting battery, you'll probably jack up the cells and have to replace it.
