Microsoft today confirmed that it will in fact have a software fix for Surface Pro 3 models affected by the Simplo battery issue, and it's internally testing the update now.
The issue started to gain public attention in July. Users were complaining that after taking their Surface off of the charger, the battery would die very quickly. Even worse, for many of these users, their warranties had recently expired. Microsoft rolled out a firmware update a few days later, and another a few weeks later, but neither of them fixed the issue.
The issue only seems to exist in Surface Pro 3 devices that use a Simplo battery. Other variants use LGE.
In an Answers forum thread, Greg from Microsoft said the following:
Thanks for your patience as we’ve worked though the details here. We can now confirm that this Surface Pro 3 battery capacity question is not a hardware issue, but one that can be addressed with a software update. Our team has been working on, and is now testing, an update that will address this. We’ll publish the update as soon as it has passed our quality assurance process. For now, you should not consider replacing your device as an update is pending.
Thanks again for your input on this. We appreciate it and we’ll share more when the update is ready.
If your device suffers from this issue, you've likely been patient with it for a long time. We likely won't see the update over the weekend, so you'll probably have to wait just a few more days.