Just got a new Samson Wireless Mic that eats through 9 Volt batteries a little (a lot!) faster than I would like. Plan to try some rechargables, I have found a rechargable that advertises it's for use in Wireless Mics....the mAh rating is about 305. Anyone know the mAh rating on a Duracell or Energizer 9 Volt? I know how long they will run and that would give me an idea of how long the rechargable would last. Thanks in advance.