There is, as @OverZealous pointed out, but I picture getting back to the truck after a hike, messing with a multi tool to open the frunk, getting the jump battery from the frunk, and connecting to the rear leads. I’d rather just take the jump battery with me.Is there a manual back up way to access frunk? Tunnel in case there's no power?
I never had to consider this before since I’ve never owned a vehicle without a way to gain access to the interior with only a key in case of a dead battery. Even my Corvette with electric door latches had a mechanical lock for the rear hatch above the license plate, a lever to open the driver’s door from the (now open) rear hatch area, and a hood release once the driver’s door was open. This gave a way to gain access to the vehicle interior where you could store a jump battery and the place to connect the jump battery with no tools required, just a key.
If there were a way to add a mechanical lock override for the frunk that would make this a lot easier. Maybe something like this emergency release lock typically used for garage door openers to pull the manual release from outside. It could be mounted in the front fender liner or under the bumper with a watertight cover. Then we’d have key access to the frunk in the event of a dead battery.