I tried an inverter (Powertech 150w) for my lappy, but the power drain was horrendous. Despite a "claimed" 90% efficiency at full load (150w output), the efficiency at lower loads (eg. 30w) was extremely poor ... my measurements with a shunt ammeter suggest about 30%.
Drain on my 12v jump starter using my inverter was about 10amps (versus under 3 when using my $20 laptop DC-DC converter).
If run my inverter (for laptop and 450D camera) off my jump starter ... along with my HEQ5Pro mount and assorted USB devices (GPUSB, guide camera), then it would be flat in a few hours as opposed to running all night ... when the weather warms up that is.
