Another option would be to plug the OS power supply in to an UPS. Even the most basic UPS will run the OS for a few days on just battery power. If you make use of the weather features then plugging your modem and router in to the UPS will give you about 24 hours of run time on just battery. My personal setup is like this and it’s great for keeping the system stable, and it has the side benefit of providing power smoothing to the OS, so power spikes and brownouts don’t cause hard to trace problems.
If your OS is setup in a box outside there are even UPS devices meant to be rack mounted or fit in to the Orbit style boxes. I honestly recommend it even if you don’t have power issues. The small cost does a lot to protect your devices, as even in the best areas power from the wall fluctuates and can cause problems for micro controllers that could lead to premature failure.