You run on batteries? Odd!
Possible reasons that I can think of:
1. There's no power to the mains socket (due, say, to a blown fuse) - try plugging something else into it to test it.
2. The charging unit is dead. If you've got a multimeter, check that there's power at its output.
3. The charging unit is a third party one, which didn't come with the laptop (or whatever else you're referring to - you've not told us) and isn't powerful enough to provide a charge at a rate faster than power is being drained from it. [
https://support.microsoft.com/en-us/help/4040260/windows-10-pc-charging-slowly ]
4. The fan isn't working on your laptop (or whatever) has stopped working, resulting in the CPU overheating and requiring extra power (in excess of what the charger can provide).
5. There's a fault with the battery, meaning that it can't accept a charge at a rate greater than that at which it's providing power to the laptop (or whatever).
Of that lot, I reckon that No. 5 might be the most likely (unless, of course, you've just switched to using a third party charger).