Did you use one of the recommended Maha chargers for 9.6v batts? Supposedly regular 9v chargers will not charge the higher voltage batts completely. Also, new NiMH batteries require several usage cycles (charge, drain, charge again) to 'form' and reach their full capacity. From what I've read some need up to 10 cycles to reach their full potential.
I just ordered four Maha 9.6V's (and a bunch of low self discharge AAs & AAAs) anlong the recommended Maha chargers yesterday, so I'm not speaking from experience but I did a good bit of research last week. The Maha 9.6v batts have a 230 mAh rating. Disposable alkalines generally have a higher mA rating so should last longer, but the voltage
may taper off more over use. For my application (Church Audio CA-Ugly preamps) I want the slightly higher, steady voltage and flatter discharge curve and as long as I can get enough runtime its all good.
Enough being the key word of course. Time will tell.
Here's a link to discharge curves and mAh ratings for standard Alkaline 9Vs under various high current loads. I'd like to find the same for the rechargeables.