Hi,
It may be that you just need a new battery.
If possible run a [https://www.laptopmag.com/articles/check-chromebook-battery-health|battery health check] and compare the ''Design Capacity'' versus the ''Last Full Charge''. Also check the cycle count, as mentioned in the link once it is >400 it may not last long.
If it is determined that the battery needs replacing, here's the ifixit [guide|85481] guide. Search online for ''AC15A3J'' to find suppliers of the battery that suit you. The battery model number is printed on the battery if you wish to verify that the model number of your battery is the same as in the guide.