`/sys/class/power_supply/AC` is hardcoded, which is not always in accordance with reality.

I installed the latest release of this software, version 1.1.0.

When I run `batwarn -d`, it fails with

```
Cannot open /sys/class/power_supply/AC/online
```

My external power supply is present at  
`/sys/class/power_supply/ADP1/`.

So I think you need to adapt your software so that the power source directory (and also the battery directory) can be manually selected.

Regards!
