I bought an external battery to use with a SD MixPre-D. The battery is rated at 98 watt hours (26400 mAh). I was told that the MixPre-D draws about .09mA (without P48) and my mics (Josephson C42mp) are rated 48mA (I would assume each) and the battery and MixPre-D are both 12 volt.
So my question is how long should I expect the battery to last?