My Macbook Pro (Retina 13" late 2013, OSX 10.10.5) has fine battery life overall - this is not the problem.
However, when the battery drops below about 8%, and before I normally get any "your Macbook will shut down soon" messages, average CPU use (over all processors) begins to go from a background low level (<10%) to >50%. It gets laggy, fan turns on, and so forth. Estimated battery life will go from 40 min to < 10 min.
Looking at activity, the main culprits for the increase can be 'windowserver' or 'mds' or 'mds_stores', often running at 80-90% on one processor, but typically other running apps (Chrome, QGIS, Evernote, etc) seem to also have a much higher usage during this period, adding up to a total CPU load >50% (and consequent temps / fan use, lag).
This doesn't seem to be a speed stepping issue, nor are any new processes suddenly appearing.
Here are some more examples of the processes, taken more at less at random after the battery went below 10% and the total CPU started exceeding ~75% - the highest processes are often mds* but other apps also increase CPU by 10x: