Tesla is expected to show off a self-driving electric semi truck next month, and a new report reveals just how long it may hold the charge. Reuters reports that this battery powered big rig would have a working range of 200 to 300 miles. That means these trucks are good for regional deliveries, They won't be doing long hauls between states. Tesla chief executive Elon Musk has promised we'll see a prototype in September, teasing it back in April in a tweet. But he's also talked about the concept since last summer. As for the self driving part, it wouldn't be the first. That honor belongs to Freightliner, which has been testing self driving semi trucks on public roads in Nevada since 2015. There's also a start up company called Change. It's working on electric delivery vans. But Tesla's Big Rig could have some extra pizzaz at least when it comes to entertaining drivers. There are several reports that the company is working on its own music streaming service for its electric cars. And for the first time we're seeing screen shots. That offer more proof. The blog electrek found hidden code for something called TTunes in the car's media app update. I'm Bridget Carey, and for all the must-know news head to CNET.com