BERLIN—The slew of new laptops shown off at the IFA trade show here are headed in the right direction—with one exception.

Windows laptops, whether conventional screen-and-keyboard models or hybrid designs that can be folded up to use as a tablet, have gotten thinner and lighter even as their battery lives have increased.

But one upgrade to these machines could prove more problematic than it’s worth.

Thin or light

Acer opened IFA with a Wednesday-morning introduction of its newest laptops, one improbably thin and the other unusually light.

Its Swift 5, available in December for $999 and up, weighs 2.1 pounds — light enough to feel like an old-school laptop without its removable battery, and lighter than almost every laptop with a fixed keyboard. Despite that, the Swift 5 offers one USB-C port, two standard USB ports, a USB-C port that can charge the laptop, an HDMI output to connect a TV and a headphone jack. Apple’s (AAPL) lighter Macbook 12-inch, meanwhile, offers just a USB-C port and headphone jack.

Acer estimates its battery life at “only” eight hours, which has become subpar over the last few years.

That Taiwanese firm’s Swift 7 was already among the thinnest laptops around, but the revised Swift 7 the company showed off is even thinner at just .35 inches thick. Getting its computer that slim, though, required Acer to make some compromises: The 13.3-inch isn’t touch-sensitive, there’s no Windows Hello face- or fingerprint-recognizing login and you only get two USB-C ports and a headphone jack.

Acer didn’t announce a price or availability for the 7.

Recharge tomorrow?

Lenovo’s thicker, heavier Yoga 920 hybrid laptop offered a different way to cut down on your daily computing payload: A 15.5-hour battery life.

(Dell’s just-updated XPS 13 laptop, starting at $800 and going on sale Sept. 12, touts the same 22 hours of battery life as the current model but can’t be folded into a tablet.)

The $1,330 Yoga 920, which features a 13.9-inch screen and weighs 3 pounds, offers both USB and USB-C ports, so you won’t have to fish out a dongle to plug in older hardware. It also recharges via USB-C, which means you can use its charger to revive many new Android phones or replace it with a smaller, lighter third-party charger if you want.

If only the same were true of the other refreshed models Lenovo had on display: The cheaper Yoga 720 hybrid laptop and the Miix 520 tablet both have proprietary power ports, even though they include USB-C ports to connect things besides their own chargers.

Dear PC vendors: Unless you can design a power connector that safely falls free if tugged hard — like Apple’s now-abandoned MagSafe or the one on the Microsoft (MSFT) Surface Pro — please accept the limits of your creativity and stick to USB-C.