Dell Inspiron 7537 Won't Power On?

I've just done a clean install of W10 on my Dell Inspiron 7537 laptop. I turned off the laptop last night when the battery was about half discharged.

I tried turning on the laptop today after it had been off 18 hours and it was completely dead - there was no response to the power on button and no charging light despite the charger outputting the correct voltage.

I read online about removing the battery so I did this. I removed the battery, pressed the power button for 60s then plugged in the power lead and hey presto the laptop started! I then put the battery back in and started W10 fine. The battery showed 56% charge so the battery wasn't flat.

I'm mystified why this happened - does anyone have an explanation? I can only think there was a poor battery connection which prevented the laptop starting and removing and replacing the battery cured this.

Does anyone know why my laptop would refuse to power on in post 1? Could it be caused by a software problem connected with the sleep state or simply a case of a poor battery connection?