A plug-in hybrid electric vehicle with a propulsion system comprising: - an internal combustion engine (110; 210; 310) for driving a pair of wheels on a first axle (118; 218; 318); - a transmission (116; 216; 316) drivingly connecting the internal combustion engine and the wheels on the first axle; - at least one electric motor (114; 214; 314) for driving a pair of wheels on the first axle (118; 218; 318), said at least one electric motor (114; 214; 314) being configured as a starter-generator (114; 214; 314) mounted on the internal combustion engine crankshaft, between said internal combustion engine and the transmission; - a main battery pack (132; 232; 332) connected to at least one further electric motor (124; 224; 324) arranged to supply electric power for driving the wheels on a second axle (128; 228; 328); - a power electronics unit (122; 222; 322) connected between the main battery pack (132; 232; 332) and the at least one further electric motor (124; 224; 324) and arranged to convert electric power from the main battery pack from a first voltage to a second voltage; wherein the power electronics unit (122; 222; 322) is further connected between the main battery pack and the starter-generator and arranged to supply electric power for starting the internal combustion engine; and - a first transformer unit (149; 249; 349) connected to the main battery pack (132; 232; 332) and arranged to supply a charging current to the main battery pack when connected to an external source of electricity, - at least one additional battery (150; 250; 350) connected to the starter-generator (114; 214; 314) and arranged to supply electric power for starting the internal combustion engine (110; 210; 310), wherein the power electronics unit (122; 222; 322) is arranged to detect the state of charge of the main battery pack (132; 232; 332), and wherein the power electronics unit is arranged to disconnect the main battery pack if a malfunction is detected and to connect the at least one additional battery (150; 250; 350) to the starter-generator (114; 214; 314) and start the internal combustion engine (110; 210; 310) if the main battery pack (132; 232; 332) is disconnected. - an internal combustion engine (110; 210; 310) for driving a pair of wheels on a first axle (118; 218; 318); - a transmission (116; 216; 316) drivingly connecting the internal combustion engine and the wheels on the first axle; - at least one electric motor (114; 214; 314) for driving a pair of wheels on the first axle (118; 218; 318), said at least one electric motor (114; 214; 314) being configured as a starter-generator (114; 214; 314) mounted on the internal combustion engine crankshaft, between said internal combustion engine and the transmission; - a main battery pack (132; 232; 332) connected to at least one further electric motor (124; 224; 324) arranged to supply electric power for driving the wheels on a second axle (128; 228; 328); - a power electronics unit (122; 222; 322) connected between the main battery pack (132; 232; 332) and the at least one further electric motor (124; 224; 324) and arranged to convert electric power from the main battery pack from a first voltage to a second voltage; wherein the power electronics unit (122; 222; 322) is further connected between the main battery pack and the starter-generator and arranged to supply electric power for starting the internal combustion engine; and - a first transformer unit (149; 249; 349) connected to the main battery pack (132; 232; 332) and arranged to supply a charging current to the main battery pack when connected to an external source of electricity, - at least one additional battery (150; 250; 350) connected to the starter-generator (114; 214; 314) and arranged to supply electric power for starting the internal combustion engine (110; 210; 310), wherein the power electronics unit (122; 222; 322) is arranged to detect the state of charge of the main battery pack (132; 232; 332), and wherein the power electronics unit is arranged to disconnect the main battery pack if a malfunction is detected and to connect the at least one additional battery (150; 250; 350) to the starter-generator (114; 214; 314) and start the internal combustion engine (110; 210; 310) if the main battery pack (132; 232; 332) is disconnected.