If Win10 is installed, try creating a Win 10 battery report and check the Design Capacity value versus the Full Charge capacity value to get an idea of the status of the battery.
If the battery still can’t be detected when trying to get a battery report then the battery may have failed and it needs replacing.
Replacement batteries are available online. Just search for Advent Monza T100 red battery to get results for suppliers.
Try the following to see if the problem can be isolated further:
i). Check the status of the battery as shown in Device Manager.
To get to Device Manager, press the Win key + x key (both together) and click on the Device Manager link in the menu box that opens.
When Device Manager opens scroll down and click on the > symbol to the left of Batteries, to expand the list.
If there is a yellow exclamation mark next to the Microsoft ACPI-Compliant Control Method battery entry then there is a driver problem. Right click on the entry and select Update driver and follow the prompts. You need to be online to do this.
If there is a red cross next to the Microsoft ACPI-Compliant Control Method battery entry then it has been disabled. Right click on the entry and select Enable. Restart the laptop in the normal way i.e. Start > Power > restart and then check if the battery now charges etc.
ii). If still no good, reinstall the battery in Device Manager.
Right click on Microsoft ACPI-Compliant Control Method battery and select Uninstall and follow the prompts. When completed, restart the laptop and let Windows “find” the battery again and reinstall it. When the laptop has restarted (give it a bit more time than usual) go back into Device Manager and right click on Microsoft ACPI-Compliant Control Method battery and click on Properties. Check what it says in the Device status box in the General tab. A properly installed battery will say “ This device is working properly”. Also maybe update the battery drivers again as shown above just to be sure.
iii). If still no good, try a clean boot and check if it now charges. If it does then it is a software problem somewhere.
iv). If still no good try starting in safe mode with networking and check if it now charges. If it doesn’t, then it is a hardware problem so as suggested try changing the battery first.