docs(battery): correct not_charging_icon description

Author: Ezequie1Sc

website/docs/segments/system/battery.mdx

@@ -46,7 +46,7 @@ import Config from "@site/src/components/Config.js";
 | `charging_icon`     | `string`  |         | icon to display when charging                                           |
 | `discharging_icon`  | `string`  |         | icon to display when discharging                                        |
 | `charged_icon`      | `string`  |         | icon to display when fully charged                                      |
-| `not_charging_icon` | `string`  |         | icon to display when fully charged                                      |
+| `not_charging_icon` | `string`  |         | icon to display when on AC power                                        |
 
 ## Template ([info][templates])