Hi Peter
I would recommend not using widgets for this. Instead you should create an app called something like "Devices". You can then use the API to populate this app with the devices you have and update f.ex. a progress field with the battery level remaining. Then when the device is almost out of battery, you can use the API to create a task on that device and assign it to the secretary. She can then complete the task when the battery have been exchanged.
I know this is most likely some more work, but I think it would be a much better solution.
We don't support widgets with any kind of custom code, so that is not an option I'm afraid.
Christian