Meshtastic messenger devices require only a low voltage power source in order to facilitate long range, text based communication between two or more nodes.  Most of the currently available devices require the user to connect to the device with either a phone, tablet or PC, via Bluetooth, WiFi or USB, so these devices should also be taken into account in regards to power. However there is a small selection of standalone devices on offer, these all-in-one options don't require the use of a computer or smart device.