I installed a new battery in my Dell 7559. It was 56% to begin with. I plugged in the ac adapter and charged all night with the computer turned off (I read that is the best way to charge...is that correct?). This morning the battery is 3%. Could there be something wrong with my laptop? This is the 2nd battery this happened with - both from the same seller on Amazon. It could be their batteries are bad, but I want to see if there is anything I can try before returning. I'm running Win 10.
So what caused you to replace the battery in the first place? Was it draining fast?
It's possible the battery you bought is faulty or it could be that your laptop has an issue. It could be to your brick the charger cord isn't working right anymore and in fact the battery itself is fine. If the brick isn't working correctly it won't charge the battery. Given you've tried multiple new batteries with the same result and are charging without the laptop on my next suggestion is to look at the charger.