Ford, the maker of the all-electric F-150 Lightning, Mustang Mach-E, and E-Transit, has filed for a rather interesting patent for a huge, roof-mounted backup battery that could top-up the main high-voltage pack of an EV when driving through an area where there aren’t any chargers available.

First spotted by RDale on the Lightning Owners forum, the document submitted to the United States Patent and Trademark Office (USPTO) shows a Bronco-like SUV that has a roof rack on top of which sits something resembling a conventional roof box. However, a charging cable sticks out of the back of the box, making it look more or less like a backup battery one would use to recharge a smartphone.

The patent application says that the backup battery could be installed when preparing for a trip where charger availability is scarce and uninstalled after returning home, where the owner presumably has an EV charger installed to top-up the main high-voltage pack.

Gallery: Ford patent for roof-mounted EV backup battery

“The backup battery assembly includes a plurality of battery modules and a connection port," the application reads. “A cordset can be used to electrically couple the backup battery assembly to the electrified vehicle by engaging the connection port of the backup battery assembly and the charge port of the electrified vehicle.”

Additionally, Ford says that the roof-mounted backup has air ducts on both sides of the housing to improve the cooling of the cells and that they can be fitted with remotely operated valves that can be closed to stop water, extreme cold, or sand from entering the enclosure and potentially damaging the batteries.

The housing shown in the patent application includes a lid and a tray lined with polyurethane foam to help manage thermal energy levels within the enclosure and keep the interior of it relatively cool.

The Blue Oval carmaker writes that the backup battery can be charged in the same way as the EV, via the available cordset, but what’s interesting is that the roof-mounted energy box is designed to include a controller module that “can communicate wirelessly with a communication module of the electrified vehicle to control the recharging of the traction battery pack from the backup battery.”

In other words, it looks like the power delivery from the backup pack to the main high-voltage battery would be seamless, without any intervention from the driver, which is a nice feature to have.

It’s a cool concept that could solve the problem of off-roading with an EV, but there is one problem: weight. It’s known that lithium-ion batteries are quite heavy and that top-heavy vehicles have a tendency to tip over, especially at high speeds. So it would be a case of driving slow and far (with the backup battery installed) or fast and not very far (without the backup pack).

As always, we’d like to know what you think about this, so head over to the comments section below to give us your thoughts.

Got a tip for us? Email: