But then why tow around that huge, expensive engine if you’re not using it? Tesla makes a 300 mile Semi as well. A 100kWh hybrid battery would experience a lot harsher cycling conditions than a larger battery in a pure electric Semi would.
I guess it's a question you'd need to ask the 1000s of customers who have bought existing HEV and PHEV trucks, not me. There's clearly some niche for them. Anyway if we're going to talk about "dragging around" something then obviously the main thing we are going to discuss is 5 tons of dead batteries, not a teensy little diesel drivetrain that maybe weighs 1 ton or less.
The idea that extra battery capacity is “dead weight” is a common misconception that belies a common ignorance about the electrical and chemical properties of batteries.
For a given chemistry and power and voltage, doubling a battery’s capacity will halve the battery’s internal resistance, thus improving its charge and discharge efficiency (as well as increasing the maximum charge and discharge power). It also halves the “C-rate,” thus allows it to last more cycles… and because the size is doubled, the number of miles per cycle also doubles. You can also afford to operate the battery with much larger margins, in its optimal state of charge, going from 75% to 25% state of charge, instead of hammering it from 100% to 0% (which would quickly wear it out, not even counting the difference in C-rate).
Sure, this still needs to be balanced with weight and cost, but a larger battery than you strictly need is NOT, in any way, merely “dead weight” in the way the ICE engine and fuel tank is in a PHEV like the Volt when I drove it for 6 months at a time while never using the engine.
