One of the hotly debated topics around Apple's 2016 MacBook Pro lineup of laptops is battery life. For some users, it's sub-par, far worse than on the previous generation of MacBook Pros. On the other hand, it achieved stellar results, with average battery life above 15 hours after Apple fixed an issue which caused erratic results on the initial battery tests.

So which is it? It could, in fact, be both, and macOS app developer Ben Slaney explains how.

In a blog post published last week, Slaney -- who develops a macOS battery life indicator app called Battery Guru -- says that the power efficiency on the 15-inch, 2016 MacBook Pro is excellent, far better than on previous MacBook Pros.

Here's the trick, however: Apple managed to significantly decrease the power draw of the new MacBook Pro under low power usage conditions -- basically when the computer is idle. So if you're just reading an article on a website, with nothing going on in the background, you can expect the battery to last up to 18 hours, according to Slaney's calculations.

"I’m impressed that the new MBP will happily sit at a 500 mA power draw for long stretches of time. This is a greater improvement than I would have thought possible," wrote Slaney.

What about the professionals and the power users?

Under heavy load, however, the power draw is similar to the earlier generation, but the new MacBook Pro has a 25% smaller battery, so when you push it hard, you won't get great results. This is likely why some pro users are dissatisfied with the new MacBook Pro's battery life. They do a lot of intensive tasks, and in that scenario, Apple's optimizations don't help much. What's needed is, simply put, a bigger battery.

Many professional users don't like the direction Apple has headed, but Slaney argues it's not that big of a deal. "Personally I wish that Apple would make huge laptops which weigh 10 pounds with dual graphics cards in them," he told Mashable in an email. "However, given the angle that they have taken (...), I think the concerns about battery life are overblown."

Slaney points out that his results are observational and aren't based on rigorous testing. But they do explain the discrepancies we've seen in the new MacBook Pro's battery life, depending on who's using it.

So if you own a 2016 MacBook Pro or are considering buying it, what should you do? One thing you can do is monitor your battery drain -- Slaney's Battery Guru will do the trick, but there are other apps that do something similar -- and see if the apps you use daily are big battery hogs. If they are, and there's just no replacing them, the new MacBook Pro likely won't make you happy.

On the other hand, if you typically don't use very CPU-intensive apps, and you don't mind checking your Chrome tabs (a frequent battery drain culprit) for power hogs and killing them every once in a while, the new MacBook Pro's battery might last well beyond Apple's advertised 10 hours.

Here's another thought. According to Slaney, macOS Sierra already supports external batteries; if Apple were to release one (third party manufacturers already have, but none of them are certified to work with the Pro, only the 12-inch MacBook), you could just plug it into one of those USB-C ports on the new MacBook Pros and get a big battery life boost. True, that kills a lot of the joy in having a super-thin laptop, but if you don't mind the extra bulk, it could be a good compromise.

Slaney agrees. "I really think that very soon there’s going to be first party or third-party absolutely fantastic power banks for these things, by virtue of the USB-C port."

And when USB-C power banks become ubiquitous, Slaney claims, the internal battery life on a portable life will become "less important."