Unfortunately, the first of two promised software updates to resolve battery issues on the Nokia Lumia 800 Windows Phone hasn't gotten rid of the issue entirely. While users wait for the second update, Nokia has detailed exactly what it believes is the cause of the poor battery life issues in a statement on its support forums. The company says that the issue is entirely software-based, with "certain variants" of the Lumia 800 unable to "access the full battery capacity."

Owners can actually check to see if their phone is affected by the issue, Nokia says, by accessing a diagnostic tool from the dialer and checking to see if the full charge capacity reads less than 1000mAh. The software update, originally promised for January of 2012, should resolve the issue. If that wait seems too long, however, Nokia is offering replacement phones in the meantime.

The battery issues on the Lumia 800 have been a dark spot on what is an otherwise well-received phone. Nokia will want to get the issues sorted out quickly — if the rumored LTE version of the phone gets released, it will definitely be needing access to every last milliampere it can get.