I'm seeing similar symptoms on my EE. It feels like the battery is generally giving me a solid lifespan- 8 hours intermittent sleep/use with WiFi on constantly- but the software battery display shows maybe 2x what it should. I've seen the "15% battery" popup flicker a few times, and had power cut out twice, both after leaving the device on for 8 hours, both with the battery reporting ~65% when I plugged in the charger and powered on. I've spotted the red light once, but having only seen it once, I couldn't say anymore whether it was a fast blink or a slow blink.
For anyone who has gone to tech support about a battery issue, is the prognosis usually the battery itself, or the EE hardware? I don't want to drag this thread down into the ambient politics, but suffice to say I like my EE enough that I'd rather shell out for a second battery and keep the flaky one around as a spare, or just accept that I need to convert the battery display in my head from now on, than send my whole already-somewhat-customized unit back for a multi-week repair/replace with the company on ambiguous footing...

Edit: In the spirit of "it will be useful to have regardless, and they may need the money more than I do right now," I went ahead and ordered a spare. I'll try to remember to post back once it arrives as to whether I end up with 1 battery that works perfectly or just two that work to 50% :P