@no1auntie_whu, a factory reset may very well help the battery drain issue, but before doing so I'd recommend trying some of the steps suggested in the link below:
As suggested by @Bindex, it'd also be worth running a Diagnostic test on the Samsung Members app. To do this, follow these steps:
> Tap on "Support", located on the bottom right of the screen while on the main page of the Samsung Members app.
> In the section named Phone diagnostics select "Get started". If you do not see this option then simply tap anywhere in the box.
> A diagnostic test (which checks all the services on your phone) may start automatically running. You can go through all of these, if you wish, by following the on-screen instructions. If you do not wish to do this, press the Back button on your Navigation bar and select "Stop diagnostics".
> Select the "Battery status" option and follow the on-screen instructions.
If the result comes up as "Action required" then this pretty much confirms a hardware fault with your battery, so you'll need to arrange for an engineer to carry out an inspection.
If you are located in the UK you can do this via the link below:
https://www.samsung.com/uk/support/repair/
If you are in Ireland, click here:
https://www.samsung.com/ie/support/repair/
If you live outside these regions, you can find your local support team from the link below:
https://www.samsung.com/uk/function/ipredirection/ipredirectionLocalList/
