pending-charge state should be mapped to icon-name battery-full-charged-symbolic
The pending-charge state means AC power is on but the battery is not being charged because its charge is above a certain threshold, to avoid short charging cycles and prolong the battery's life. From the user's perspective this is equivalent to the situation where the battery is fully charged, so the icon should reflect that.
In addition, on certain laptops the battery management hardware will report (through ACPI) the status as fully-charged instead of pending-charged when this situation is reached. This was seen on a Lenovo Yoga 900.