The Jeep Wrangler is famous for its ability to tackle brutal off-road conditions. It's also known for the fact that, generally, it doesn't change too much. Today's flat-sided Wrangler is clearly a descendant of the boxy Jeep that slogged through the battlefields of World War II.

But Jeep will soon undergo one of the biggest transformations of its 79-year history. At the CES technology show in Las Vegas next week, Fiat Chrysler Automobiles will unveil plug-in hybrid versions of the Jeep Wrangler, Cherokee and Compass. The plug-in models will bear a new 4xe badge, which is a play on the term 4x4 used to denote four-wheel-drive vehicles.

Fiat Chrysler CEO Mike Manley has said previously that a plug-in hybrid Wrangler will go on sale later in 2020.

Fiat Chrysler currently offers two plug-in hybrid models, the Chrysler Pacifica Hybrid minivan and the Jeep Commander PHEV, a crossover SUV sold in China.

Batteries in ordinary hybrid vehicles are charged as the vehicle drives, particularly during braking, and that power is then used to turn the wheels together with power from the car's gasoline engine. In most hybrid vehicles, the electric motors can even drive the vehicle by themselves in situations where not much power is needed, such as at low speeds.

In plug-in hybrids, like the Pacifica Hybrid, the batteries can also be charged using a power cord. After being charged this way, the vehicle can be driven for a number of miles on electric power only. (The Pacifica Hybrid can go 32 miles using only electricity after a full charge.) Beyond that electric-only range, it will operate like a hybrid vehicle, with both gasoline and battery power using internally generated electricity

Fiat Chrysler has not said how the plug-in hybrid systems will be designed in its new vehicles. The Cherokee and Compass are crossover SUVs, meaning they have car-like engineering that's been modified for off-road use. The Wrangler is fundamentally different. It's engineered like a truck with a rugged frame and simple suspension systems that give the Wrangler a bouncy ride, but one that's ideal for off-road conditions. Also, the Cherokee and Renegade are available in versions not designed for serious off-road use, while every Wrangler is expected to be capable of operating in rugged conditions. The Wrangler may need a fundamentally different sort of plug-in hybrid system to satisfy hard-core off-road enthusiasts.

All Jeep models, including the larger Grand Cherokee, will have electrified power options, which could mean fully electric or hybrid versions by 2022, FCA said in its announcement.

The Jeep Wrangler is already available as a "mild hybrid" with small, light batteries, but the batteries don't provide enough power to drive the vehicle on its own. Instead, they provide some additional power to assist the gasoline engine during acceleration, helping to save gas.

After the new plug-in hybrid vehicles are unveiled at CES, more details like pricing are expected to be provided at future auto shows this year, FCA said. FCA recently announced plans to merge with PSA Groupe of France, which owns Citroën, Peugeot and Opal.