I have an HP EliteBook 840 G8 Notebook PC, and the battery has lost its charge.
So I bought a new one. I bought one from Trademe as that seemed the easiest choice.
After fitting, the charge rate was not a lot better than the original 3.45 hours, so I decided to return the battery for a refund.
I'm sure the battery lasted about 8 hours when I first used the HP. 
Do I need a genuine part or perhaps a new laptop?