Hi @tingwang2013
Seems as though there's a problem with the battery in the laptop.
Create a [link|https://www.tomsguide.com/how-to/how-to-check-battery-health-in-windows-10|battery report] to check the status of the battery.
When you have the report, compare the ''Design Capacity'' value versus the ''Full Charge Capacity'' value as seen in the report.
For a good battery they should be nearly the same value.
You can work out the condition of the battery as a percentage by using the formula: Full Charge Capacity value x 100 รท Design Capacity value.
If the battery is <35% you may wish to consider replacing it.
Here's the [link|https://download.lenovo.com/pccbbs/mobiles_pdf/l14_l15_gen2_hmm_en.pdf|hardware maintenance manual], for the laptop.
Go to p.70 and then to p.84 to view the procedure to remove/replace the battery in the laptop.
Here's the [https://pcsupport.lenovo.com/us/en/products/laptops-and-netbooks/thinkpad-l-series-laptops/thinkpad-l14-gen-2-type-20x1-20x2/20x1/parts/display/compatible?linkTrack=Caps%3ABody_SearchProduct&searchType=4&keyWordSearch=L14%20Gen%202%20Type%2020X1%2020X2%20Laptops%20%28ThinkPad%29%20-%20Type%2020X1|parts list] for the laptop. Click on ''Select Commodity > Rechargeable batteries Internal(8)'' to find the spare part numbers for all the batteries that are compatible and can be used in the laptop (one of these numbers may also printed on your battery). Search online for the ''part number only'' to find suppliers that suit you best.