But it is a particularly good idea for an electric car because mains electricity can be used if the car is still plugged in, thus conserving battery power.
但对电动汽车来说这尤其是个好主意，因为如果车子仍然插在插头上，就可以使用市电，因而节省电池电力。
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Range-extenders like GM’s Volt (the Ampera in Europe) are powered by an electric motor that can be recharged either from the mains or by an on-board internal-combustion engine.
At Frankfurt GM's Opel unit showed a small diesel-electric hybrid with a battery that can be recharged from the mains to give an electric-only range of 40 miles.