“Is that for the block heater?”

Neighbour guy looked perplexed.

I was plugging the BMW X5 xDrive40e’s recharging cable into the receptacle on the front fender one night, at about 27 below.

“No, it’s partially electric. This is to recharge the battery,” I replied.

Neighbour guy perked up. He drives an F-150 EcoBoost, so I figure he’s at least slightly interested in fuel-saving tech.

“How’s that work?” he asked. “Is it a hybrid?”

Given the extreme cold, and my armful of delicious groceries, I tried to whip up the simplest explanation I could find.

I explained how this particular X5 variant worked like a hybrid by combining, or switching between, gasoline and electric power for propulsion depending on the situation. And that unlike many hybrids, this one could be plugged into the same 110-volt outlet I use for my Christmas lights, to supercharge the battery with surplus juice that delivers about 20 kilometres of gas-free driving per charge at up to 120 km/h. Non plug-in hybrids typically go a tenth of that, and only at low speeds, and only under very light throttle.

In a normal hybrid, power is constantly flowing in and out of the battery. It assists the engine, and is replenished by regenerative braking, and the gas engine’s operation, when it’s running. Electrons stream to and fro and charge levels go up and down, constantly. But the battery never builds enough excess charge to sustain the vehicle for long periods. Battery chemistry is at play, too.

I told neighbour guy that you plug in a hybrid like this one to ‘top up’ the battery, providing additional EV range and reducing fuel use.

“That sounds pretty complicated,” he replied.

Indeed it is. And I hadn’t even explained about the various selectable modes from BMW’s eDrive system, which allows drivers to dispatch the surplus charge however they like. The MAX eDrive mode locks the vehicle into electric-only mode, the AUTO eDrive function runs things like a standard hybrid, albeit with longer gas-free driving periods, and the SAVE mode locks the surplus driving charge in for use later on your voyage.

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