Hi mate,
I can't be 100% sure, but 99% sure, it doesn't draw or charge the laptop. It's only a USB device.
Laptop battery has its own life time, average about 3 years (depends on the way you use it). However, if you leave it unplugged and unused, it loses 2 - 3% daily.
They are lots on bay of e, have a look. Very good one set you back 300 ish, cheap ones about £20, but I got one for 60 and a bit which is enough for what I need. (BTW, some chinese ones got great software with it, I have seen it in my mate place, and very cheap, only thing is you have to wait for a week)
Felix
P.S. sometimes I get someone drives, so I can read the info on the laptop, very interesting reading, lots of things which I never knew could be read by ODB, such as
Engine RPM, Calculated Load Value, Coolant Temperature, Fuel System Status, Vehicle Speed, Short Term Fuel Trim, Long Term Fuel Trim, Intake Manifold Pressure, Timing Advance, Intake Air Temperature, Air Flow Rate, Absolute Throttle Position, Oxygen sensor voltages/associated short term fuel trims, Fuel System status, Fuel Pressure
Many others...