I went home for Chrismas, I got my laptop with me but forgot its charger in my renthouse. Battery is old and it takes about 10 mins for it to run out of power.
What am I supposed to do now?

Btw Merry Christmas!

Build a time machine. Go back in time. Tell yourself to take the charger. Get back to your timeline, but you'll still not have your charger, because the event of taking the charger is in a different timeline, and in your timeline you didn't take the charger with you, but at least you in different timeline has it. 😋

Exchange gifts for a charger

Do you have another wall plug, transformer and some spare wire?

I wouldn't recommend it though. Buy a new battery and charger (depending on when you go back to your rental).