You may think the two have a correlation, but you’d be off slightly. Handheld vacuums tend to be much lighter, slimmer, and are designed to easily be held by your hand, whereas cordless vacuums are much chunkier items which run off a charged battery after you’ve taken them off a wall mount in your home.
In short, they’re for slightly different purposes. If you’re going for a deep clean throughout your car, a cordless unit will be better suited. They can pick up more dirt and debris from your vehicle where handheld units can either run out of charge or only pick up so much. While testing the Black and Decker vacuum, I attempted to vacuum out the back of a car, but it died after doing the rest of the interior and a bit of my house.

There are few if any, brands producing handheld vacs specifically for car care, but luckily, there are still plenty on the market designed for wider applications that'll do just fine. Look out for some great examples from Bosch, Gtech, Shark and Black and Decker.

In most cases, you'll be struggling to surpass the 20-minute benchmark. Some devices can only last 10, so you really have to bear in mind what kind of tasks you aim to do with such a device.
The Black and Decker device listed at the top among some others have a much longer life, and these tend to be the machines we prefer. We advise that you have a good think of how long you need a handheld vacuum to run in order to do the tasks in hand.