- Make sure the "M-S" switch (the little greenish slide switch) is set to M.
- Hook the battery balance cable first, then the main battery cable (in that order)
- IIRC, you have ~15 seconds from when you plug in the battery balance cable to when you plug in the main battery connector. So don't dawdle.
- Once it's all hooked up, the main LED (not the individual cell LEDs) will be on solid. Press the large-ish blue button and the main LED should blink slowly.
You should be able to charge now.