These devices only have a limited battery life, so it's best to leave them plugged in unless you're checking appliance power usage around your house.
Try plugging the device back in with the power cable provided originally.
If this doesn't work, try the following:
Disconnect the USB cable from the power port of your In-Home Display.
Leave the cable disconnected for 60 seconds.
Before reconnecting, bring the In-Home Display close to your electricity smart Pay As You Go meter.
Reconnect the USB cable to the power port of the In-Home Display.
Your In-Home Display should reconnect within 2 minutes, but if you weren't seeing any balances, these might take up to 30 minutes to appear.
If that still doesn't work, please send an email to email@example.com and the team here will help you try to get the device working again.