Why is there a x on my battery

[AC Question]

There are x on my battery when I charge it.It shows a red x

 

[hallux]

I get that on my Samsung tablet. I usually have to unplug the charger and plug it back in, sometimes a few times, to get it to not show the red X and actually charge. It's likely not the battery itself that's being a problem but more likely just a poor connection to the charging adapter. It happens more often on one of my charge cables than another.