Devices such as the MAX HD4, and the MAX HD2/4 with MediaFast accept dual DC input and support up to 8x 802.3at PoE ports. Here’s how it works:
If you plug in the first DC input, LAN ports 1-4 will offer PoE output. If you plug in both DC inputs all LAN ports (1-8) will offer PoE output.
An additional note here is that you need to use 48VDC power supplies in order to get these PoE ports activated.
Peplink’s partnumber for this 48V DC power supply is ACW-609. 
Hello @Alan, @Tim_S & @Joey_van_der_Gaag,
Did you know you can also power these and deliver the required voltages to operate the PoE Function from a 12VDC or 24VDC Source? We have successfully used a high-quality DC-DC converter to achieve this with Solar powered installations. However, it would work with mobile locations such as motor vehicles and water-based vessels.
We have been sourcing DC-DC converters from Powerbox Australia. You can see some of the selection at https://www.powerbox.com.au/dc-dc-converters, they ship internationally, and although the units are on the high side (in $), these units got designed for performance and reliability.
Happy to Help,
Marcus 
