A second plug-in hybrid version of the Mercedes-Benz SL is under development. This uncamouflaged example is under development in the Austrian Alps.
The front fascia looks the same as the one on the previously spied SL PHEV. There's a trapezoidal element with a metallic finish in the middle. Intakes with a roughly trapezoidal shape are on each side. The grille has vertical ribs, and there's an AMG logo on the driver's side of it.
Gallery: Mercedes-AMG SL 53 PHEV Spy Photos
This roadster rides on wheels with five pairs of spokes. An AMG-branded ring is separate from the rim.
Without seeing the rear, you might think this is the same as the previously spied examples of the SL PHEV. However, this car has quad, circular exhausts, rather than the square shape for the outlets on the other vehicle.
Black tape covers a portion of the charging door on the passenger side of the rear bumper.
Our spies believe this model would slot below the other SL PHEV. It might get the name SL 53, suggesting a place in the lineup that's a step below the SL 55 but above the SL 43.
The powertrain for this model is a complete mystery. One possibility would be to take the 2.0-liter turbocharged four-cylinder from the SL 43 and give it an extra boost from an electric motor. This model already makes use of a 48-volt starter-generator and has an electrically assisted turbocharger that reduces lag.
The hotter SL PHEV reportedly uses the 63 trim's twin-turbo 4.0-liter V8 with the addition of an electric motor. The result would allegedly be an 800-hp (597-kilowatt) output, which is a healthy upgrade over the 577-hp (430 kW) rating without electric assistance.
It's also not clear when these SL PHEV models debut. The fact that Mercedes is not camouflaging them indicates the company doesn't see much reason to hide them. Sometimes, this is an indication that an unveiling isn't too far away.
For a discussion about the new SL-Class, check out this episode of Rambling About Cars: