Class 668.4

Updated: August 2026 – A modern regional multiple unit with a pantograph that lowers mid-route and keeps running anyway: that’s the Class 668.4, the battery variant of the Siemens Mireo. This page explains how to tell it apart from the other vehicles in the same number block, why it’s listed under the type code for diesel railcars, and where waiting for it pays off.

What is the Class 668.4?

The Class 668.4 is a multi-part local service multiple unit with battery storage based on the Mireo platform from Siemens Mobility, marketed as the Mireo Plus B. The drive is fully electric; under overhead line, energy comes from the contact wire, and on non-electrified sections from the onboard batteries.

In operational terms, it replaces exactly what the diesel railcar has done for decades: serving lines whose electrification never paid off. The classic counterpart is a vehicle like the Class 642 – same manufacturer, same job, completely different drive concept.

Type code 95 and what it really tells you

The twelve-digit UIC vehicle number begins with two digits that describe the vehicle type. 95 denotes diesel railcars – and yet the 668.4 is listed here. That’s not a mistake, but a consequence of the system’s history.

German class numbers starting with 6 were assigned to combustion-engined railcars with the switch to EDP numbers in 1968. This assignment survived the change of technology: when battery-electric vehicles came along, they were slotted into the existing block because they take on the same operational role. How the twelve digits are structured in detail is covered fully in the article on the UIC number and its check digit.

The practical consequence: the number tells you the vehicle’s role, not its drive type. You see the drive type on the roof.

This principle predates battery technology. Even the class letters used before 1968 – VT for combustion railcar, VS for driving trailer, VB for trailer car – described what task a vehicle performed in a train formation, not how it was solved technically. The EDP numbers translated that logic into digit groups and have preserved it ever since. Anyone reading German class numbers is therefore primarily reading an arrangement by operational role. That also explains why diesel railcars, battery vehicles and special types can sit side by side in a single number block today without any contradiction.

How to identify the 668.4 in the field

A fixed order for identifications like this – first shape, then drive type, then number – is described in the guide to identifying locomotive classes.

Context in railway operations

Battery multiple units have a more narrowly defined field of deployment than diesel railcars: they need plannable charging opportunities. From that, you can work out where to look for them.

Place	Chance of a sighting	Why
Terminus of a non-electrified branch	high	Turnaround time, often with charging equipment, good view from the platform
Transition point where the overhead line ends	high	The pantograph goes up or down – the most telling subject
Electrified approach section	medium	The vehicle runs there like a normal electric multiple unit
Purely diesel line with no charging point	low	Without charging infrastructure, no scheduled deployment
Depot or stabling sidings	not accessible	Operational railway land subject to house rules, no public access

Spotting and photo tips

The smooth carbody of the Mireo family is a demanding subject to photograph: large, unbroken surfaces look flat in midday light and reflect heavily. Low light in the morning or late afternoon, on the other hand, draws out the edges and gives the front a more three-dimensional look.

There’s also a problem shared by all modern regional multiple units: they look like each other. A shared design language has taken hold across manufacturers, favouring large front windows, smooth side walls and low entrances. That means a class is rarely identifiable with confidence from a front-on shot alone. If you want to keep your photo archive useful, get into the habit of always also taking a side view with a legible vehicle number – that’s the shot that answers the real question in five years’ time.

This order has proven useful in practice: first a clean three-quarter view as the main shot, then a close-up of the side wall with the full vehicle number, and finally a context shot at the point where the overhead line ends. Which focal length makes sense for that is covered in the guide to the best telephoto lens for railway photography; where good platform positions can be found in Germany at all is covered in the overview of the best stations for trainspotting.

The same applies throughout: the platform, station forecourt and public bridges are enough. Track areas and operational installations are off-limits, and barriers stay barriers.

Common mix-ups

Within the number block, the most important point of comparison is the Class 668.2, the other battery vehicle – shorter, two-part, from the LINT family. For pure diesel vehicles of similar size, looking at the roof helps: the Class 622 carries no pantograph there.

Verdict

The Class 668.4 shows how the diesel railcar’s role can change without the numbering system moving with it. The type code 95 stays, the drive type is different. That’s actually helpful for identification in the field: a vehicle with a railcar number, a pantograph and running with no contact wire can hardly be anything else. Everything beyond that – network, operator, fleet size – is subject to change and needs re-checking before every trip.