OS X 10.8.1 improves battery life considerably on MacBook computers, by as much as four hours, a registered Apple developer has confirmed for Softpedia.

A developer enrolled with Apple’s $99 / €80 annual program has confirmed to us that Apple’s latest incremental update, OS X 10.8.1, would resolve all the reported battery drainage issues when the final bits are out.

In fact, he said, the improvement is quite substantial.

“Until I installed 10.8.1, my MacBook was showing 4h:05m after a full charge,” he said, referring to the amount of time before the battery would deplete completely.

“After installing 10.8.1 it's showing over 8h,” he said. “I'm now able to use my Mac throughout the day again without having to carry my charger,” said the happy developer.

Apple is actively testing Mountain Lion betas to resolve some of the most widespread issues reported after the OS’s July 25 debut, including some potential networking issues, as well as a sound problem with MacBook Air and Thunderbolt Display combos.

Earlier this month it was confirmed that Apple had begun investigating the battery drain problem by talking to affected customers.

Select users (not actual developers) have since been offered special builds of OS X Mountain Lion (presumably the same 10.8.1 betas offered to developers) through the Apple Seed customer seeding program.

Apple has not only been able to assess what was the culprit, but it also addressed the battery drain issue in the most recent betas handed to its sea of programmers, according to our tipster.

“OS X Mountain Lion Update 10.8.1 is an update to OS X Mountain Lion 10.8,” reads the documentation accompanying the latest downloadable package, OS X 10.8.1 Build 12B17.

At the time of the seeding (August 17th), the Cupertino giant instructed developers to focus their testing efforts on areas such as Active Directory, iCal, Microsoft Exchange in Mail, PAC proxies in Safari, SMB, USB, and Wi-Fi.