Following along on this thread, if you try out the powerex batteries and they work, let me know - 9V have been getting wasteful with my SX-M2, which is a shame because this pre sounds so darned good.
Powerex 9.6 volts on the way so i will report back when finished testing.
The in-use voltage of the 9.6V NiMH Powerex batteries is much closer to that of alkaline 9V's than other rechargable "9V" NiMH batteries, most of which provide a lower voltage.. if that matters in the Sx-M2. They also provide greater current and storage capacity and are more reliable. I've had better success using them than standard alkaline 9Vs in other preamps. And as a side benefit they eliminate potential leakage.
The caveat is they tend to fail rapidly after a couple years of use. They key to predictable use and replacement is to catch that before it happens by getting in the habit of measuring voltage while in-circuit, before and after each recording session. The voltage curve is much flatter than alkaline, but when you start to see voltage dropping afterward earlier than expected, replace them.
There may be 9.6V NiMH from other than Powerex available now. The higher voltage is due to them containing an additional NiMH cell. Most of them including Powerex these days should be low self discharge (LSD) type, which is what you want for reliability. I believe the current LSD Powerex 9.6Vs still have a black case with yellow lettering. The older non-LSD versions had a white case with black and yellow lettering. Use a good smart charger, measure voltage to monitor aging prior to end of life, and you're good to go.