Several people have asked if I will be testing and reviewing 9v rechargeable batteries anytime soon. The short answer is no. I only have one device (a PSM600) that uses 9v right now, and hope to replace that by summer. Still, I’ve used a lot of 9v batteries in the past, so I’ll put up some thoughts and recommendations here.
First, I’ve had great success with Ansmann 250 mAh 9v batteries and chargers. I’ve used the 9v cells in ULX mics from Shure as well as PSM600s and PSM700s. Run time was always more than two services, and as long as we changed them regularly, they never failed us. The batteries themselves lasted a long time; I have 2 churches worth of experience at 2 years each. Given how expensive a disposable 9v is, the payback period is short.
UPDATE 10/6/13: Ansmann now makes a 300 mAh 9v battery, which I would recommend over the 250 mAh version. Horizon Battery also carries a 600 mAh LiOn battery from HiTech. According to reports, this battery will run 12-15 hours. You must use their charger, however, so be aware of that. Still, it looks like a great option if you are still running 9v batteries. END UPDATE
The question was raised about capacity of 9v batteries, and how they appear to be much less than a AA. Simply looking at mAh ratings does not tell the whole story; we need to look at energy capacity, and for that we need to convert to watts (or in this case, milliwatts). Take a 9v 250 mAh battery. The actual voltage is 8.4 volts. We know that Volts x Amps = Watts, so, 8.4 x 250 = 2,100 mW. In contrast, a AA rated at 2700 mAh works out this way: 1.2 x 2700 = 3,240.
So while it’s true that a AA cell has significantly higher energy density (which is why most mics are heading to AAs...), the 9v is not too shabby.
I’ve also use the 300 mAh Powerex batteries from Maha with great success. Do that math on those and you end up with 2,520 mW. iPower also makes a LiPolymer 9v rated at 500 mAh, which gives you over 4,000 mW. So the capacity is there—just know that run times will be a little shorter with the lower power batteries.
If you only need a few 9v batteries, look at the Maha MH-C490F. It’s a 4 position charger and runs about $30. For higher capacity, look at Maha’s MH-C1090F (8 positions, $50) or Ansmann’s 10-bay 9v charger at $70. Personally, I wouldn’t spend the extra money on the Ansmann rack mount chargers (they are over $500), unless you really need them racked.
You can find the Maha chargers, Powerex and iPower batteries at Thomas Distributing. Horizon Battery handles Ansmann batteries and chargers (and the folks there are super-helpful if you have questions).