The strength of autonomous vehicles is in simple, repeatable, high-traffic areas in which little maneuvering is necessary. There's a lot less nuance in driving a truck, outside of navigating within a city, parking, etc.
the strength of electric vehicles is in high efficiency, low-load, short distance applications in which nobody needs to go very far. People look at a Tesla and its 260 mile range and assume it's no big deal; it's a very big deal because the chemistry of batteries does not change easily.
"Better battery life" is a flippant thing to say but a formidable task. Consider: A Tesla Model S is about the same car, performance-wise, as a BMW 3-series. The Tesla, however, costs three times as much, weighs 1000 lbs more and has half the range. People are willing to accept that because it's a luxury electric vehicle (and in California, electric vehicles get the carpool lane - no small perq). But extrapolate out to a big herkin' Peterbilt. The engine isn't a big deal; big stupid electric motors will produce torque and power just like we need for hauling 40 tons across state lines. But that Peterbilt will haul no-lie 300 gallons of diesel fuel. Compare and contrast with our BMW - it's got a 15-gallon capacity and it doubles the Tesla, whose most hard-fought attribute is range. Safe to assume all the batteries they could cram into the Tesla - probably 1500 lbs worth - gives it the range of 7 gallons of gas. Gas/Diesel isn't a comparison, but remember - we want our long-haul trucks to go for days and days and days without really stopping. Even if you could slap a battery pack that big in an 18-wheeler, you certainly couldn't recharge it as quickly as you can fill up a gas tank.
Long-haul trucking will go electric as soon as there are rails in the road. Until then it's gonna be fossil-fuel powered. Trains are radically more efficient than trucks and they're diesel-electric and will be for quite some time to come.