On the other hand my old netbook has a battery...
Is it possible to trigger
For example; My netbook goes into sleep mode when there is %10 of the battery juice left but I want bitcoind to shut itself down when there is %15 left so it will be a super safe shut down. No fuck ups, no conflicts...
Or, Is it necessary at all?
You could always use a command that checks if the netbook is charging, once the charger is removed, the node shuts down. Depending on how old it is, it might take mre than ~8% ttery to shutdown on (assuming it'll shutdown after 7% is left).
Else, use 25-30% just to make it safer for the node (if it's always plugged in, then you can expect the battery to start to drain as well powerwise after a few weeks/months depending on its reliability.