need to replace the battery. keep it on a charger. (18W or higher . I am considering buying an amazon[br]
'''(Original Quality) 87W USB-C Power Adapter Replacement USB C AC Supply Charger Compatible with MacBook Pro Charger 15 Inch Laptop (USB-C Cable Included)''' for list 39.99 USD)
Get a new phone, download “files” google transfer app onto both phones and transfer everything. then sell the HTC phone for whatever someone will pay.
https://www.htc.com/uk/contact/productissue/?&family=u&index=htc-u-ultra&product=HTC%20U%20Ultra&categoryid=power-charging&content=guid-599060ae-0591-4fa1-b77f-c6a635196e49