Devices, systems, and techniques for a synchronized network for battery backup are described herein. A network device can establish a synchronized sleep schedule with the network while in a mains-power mode of operation. The network device can transmit data in the mains-power mode without regard for a transmission window of the synchronized sleep schedule. The network device can detect an interruption of mains power to itself and transition to a low-power mode of operation. The network device can then transmit data in the low-power mode, restricting data transmission to the transmission window of the synchronized sleep schedule.