Dam modern tec stuff

Why is there no warnings given I have had a mobile lap top for two and half years and I tried once to use it on just battery it last a couple of hours and so I thought stupidly I hasten to add that was no good so I got the mains lead and just pluged in. Right that was wrong over time I buggared up the battery and bingo all went wallop a week ago O well the joy of modern high tec stuff, by the way fingers burnt I learnt I know take out the battery and run this laptop on just mains, maybe the old grey box is waking up at last