Possible to power 5v relay directly from MKR1010 while running on battery?

I'm working on a project where reliability is critical, trying to avoid even 1 second of downtime on a system running 24/7. I'm controlling some solenoid valves with a solid state relay module that runs off a 5v supply. I'd like to control it with an MKR1010 because the built-in battery functionality would allow the board to keep running in the event of a momentary or short-term power outage. For the same reason, I'd like to power the relay directly from the arduino's 5v supply. However, I'm not sure if the 5v supply from the MKR can still produce 5v while it's on running off of battery, which supplies only 3.7-4.2v? I can't find any documentation of this. Is there some internal voltage booster function? It'd be useless for the arduino to continue running during an outage while not being able to switch the relay.

Another option could be to use the 3.3v line from the arduino connected to a boost converter to step the voltage up to 5v. That's assuming the 3.3v line still produces 3.3v while on battery. Maybe I could modify the relay somehow to run off 3-4v instead of 5v.

EDIT: looks like the built-in charger does have a 5v boost capability, but I don't know if that is functional or how it works?

So yes I got a LiPo battery and confirmed that, as expected the 5v output pin only produces about 3V when the arduino is powered only by the battery.

I got a $2 adjustable boost converter on ebay and connected it between the 3.3v output on the arduino and the relay, and set it up to output 5V. Now whether I'm connected to power or running on battery, I get a consistent 5v supply to the relay.

Maybe there's a more elegant solution but that was cheap and easy.

Connect the DC-DC directly to the battery.