Could be either/both. Just FYI: Most LIon battery chargers don't even try to charge above 95%, since there's a rapid loss on the return above that level. You never want to fully saturate or fully discharge a LIon anyway, as both tend to make them unstable and/or destroy the battery.

As for the 85% mark, it could be that the guestimator is off because of some recent past event. That number is a guess from the internal system, which sometimes gets out of sync with reality. If so, it should just drift back toward reality over time. Or, your battery is degraded, which happens. Worst case, buy a new one. Third party batteries with higher capacity than the stock Nokia can be had for quite cheap. There's a thread on it here in the forums for where to get the best ones, well summarized in the first 2 or 3 posts by a very active community member.