That's pretty good going really.
As the above says, it won't go on indefinitely, but I'm surprised it's done this well to be honest.
Keep using it as a laptop (i.e., not connected to the power supply 24/7), and it should do well. And ideally, do a full discharge, leave for 4 hours or so, then a full charge and leave for another 4 hours after it says it's done. Do this once every few months or so. It won't really affect the battery much, but it helps with the laptop's calibration, so it knows if the battery is truly empty or not.