With the Dell Lattitude models there is a known battery issue with the battery icon showing as an "X".
The issue can in 8/10 cases be resolved with the solution below:
1. Please remove the battery and ac adaptor.
2. Press and hold the power button for 15 seconds. Now wait for 2 minutes.
3. Please reconnect the battery and ac adaptor and power on the system.
If the solution doesn't work, please create an RMA on following site: https://tier1asset.com/rma-application-form/