Just checked, yep, 2500 mAh, but at 1.2 volts each? Weird... how does it work? haha.
You will find that most of your rechargeable batteries are 1.2V and not the 1.5V "standard". It has to do with the chemistry in the cells. If you want a more detailed answer, I am sure I can dig up the info. Anton Bauer has a great .pdf (although a
bit of a sales tool) on their battery technology for camera systems.
In the production world, there is nothing like watching the look of terror going across the audio dept when someone forgot to change the batteries in the CEO's wireless. That too is another reason NOT to use rechargeable batteries in long run, mission critical applications. I understand that batteries get pricey but do you really want your whole production to suffer because someone didn't want to spend a few bucks on fresh batteries at the beginning of each day?
Back when I was doing field audio for video, someone had come up with some replacement 9V battery cases that fit into a standard 9V compartment. They had a
pigtail attached so you could hook them up to an external battery
system.
(For those who need the details: Lectrosonic wireless transmitters in a portabrace kit along with the field
mixer connected to a single battery (NP1)
system. Used to
send audio to the camera. If I have to explain it any more, you probably wouldn't understand the
point anyway.)
Depending on your particular situation, you may be able to get away with other voltages.
DISCLAIMER HERE! Please check with the manufacturer before doing any of this because it could damage the gear, start a fire, destroy your love life,
etc.
The
voltage regulators found in many electronics are designed to take in a fairly stable DC
voltage and convert them into a fixed output. Typically these are 15, 12, 5 or 3.3 VDC. The input on these regulators MAY BE as high as 30VDC. AGAIN CHECK BEFORE YOU DO ANYTHING THAT COULD DAMAGE YOUR GEAR. That said, some gear that is designed to work off of 9VDC can safely be powered by 13.8 volt camera batteries. There are tons of these out there along with a charging
system that is specifically designed for that battery.
Depending on the size, weight,
etc of your application, this may be a cheaper alternative then something like a 9V.
In the microprocessor projects I work on, those in the know discourage the use of 9V battery sources because of the low Ah capacity. In other words, they will drive a 5VDC regulator but not for long. In these cases, they recommend 4.5V right to the
processor via 3 1.5V batteries or 4.8V via 4 1.2V rechargeables.
Now, if you really have to use rechargables for whatever reason, there are lots of battery analyzers out there that will simulate a load on the battery and give you a report of what kind of performance to expect out of it.