Microsoft has rolled out a software update for the Surface Pro 4 and the Surface Book, but it does not fix some issues reported by users.

Microsoft claims that the battery in the Surface Book and the Surface Pro 4 can last up to 9 hours and 12 hours, respectively. However, many users have complained of the battery draining out very quickly.

"I can't even leave it in sleep mode or else it will be dead the next time I use it. I set it up to hibernate but the 10 minutes before it'll usually lose 5-10 percent in sleep," complained a Surface Pro 4 user.

Owners of the Surface Book are also in the same boat.

"After work I closed the lid, threw it in my bag and headed home. When I got home I took it back out and it was warm to the touch and the battery was about 15 percent less (25-minute car ride). Throughout the night I have tested various settings but nothing seems to put it to sleep," complained a Surface Book owner.

Microsoft has released the firmware update dated Jan. 27 for the two devices, which is expected to fix various bugs including the battery drainage issue.

However, Paul Thurrot, a reputed Microsoft blogger, suggests that the latest January update for the tablets brings only a partial fix and does not address the battery drain issue when the devices are in sleep mode.

"And this does appear to be a partial fix: There's no hint that any of this will fix the single biggest issue, which is related to the new power management states that come from Skylake," says Thurrot in a post.

Some users who have downloaded the January update are in agreement with Thurrot.

"This update seems to have made my suspend/hibernate issues worse. I can't get mine to come out of sleep mode at all now, whereas before the problem was infrequent," commented a user on Thurrot's blog.

Surface Pro 4 owners have also complained on Twitter about the battery drain issues even after downloading the January update.

So after installing last nights firmware for the SP4, my Surface dropped 6% in sleep mode over the last six hours. Would you say it's fixed?

— Zac Bowden (@ZacB_) January 28, 2016

The January update will be of very little use to Surface Pro 4 and Surface Book customers who have been facing battery drain problems.

It seems highly unlikely that Microsoft will issue another update soon. Owners of the Microsoft flagship tablets will now have to wait until the February update and hope it resolves the niggling battery drainage problem for good.