To be able to charge a battery from a circuit powered by that battery then you would have invented perpetual motion, aircraft batteries, like car batteries, are only there to power circuits until the engines are running after which the engine(s) generator(s) take over all the power requirements. With your laptop it's not the battery powering it it's the mains PSU.
Presumably these batteries have to be isolated from the buss by a blocking diode otherwise uncontrolled charging will take place which will cause the battery to overheat. Could it be that there are some nasty spikes on the buss that takes the blocking diode out?