unlock symbol and "custom" when it tries to boot

[krauster]

I have an old S4 that I've been using for reading in bed. No sim card, just connected to the home wifi.

The battery was draining so fast on it that I decided to just leave the charger permanently connected and it's been working fine like that for over a year, maybe two. A couple days ago it wouldn't show that the charger was charging and the battery started draining quickly.

I do have a spare battery from when I used to use it as a phone and needed it. So I popped that one in, it charged and I was fine. Then that battery went dead with use not on charger but it won't charge up anymore when I connect it to that charger, or to another one that use for my Note 4 that replaced the S4 a while back.

With the battery that was working inserted and the phone connected to the charger when I push the power button I eventually see a black screen with an open pad lock - black dot in the middle and the word "custom" below it. This was not a rooted phone. (Although I am vague on that. I was experimenting with rooting an old Nexus pad and might have tried it on the S4 but I don't remember ever trying that. I'd say it was never rooted.)

What does this seem like is wrong?

 

[krauster]

On the other hand ----- With that device out of commission I am sleeping better. I may not bother fixing it and go back to a night life without handheld devices for my health.