I've been using these batteries in my camera for over a year now and they are still as good as new. I also recently started using them in the Wii remotes and Wii fit balance board and the performance is amazing. It has been over 3 weeks and still no need to charge them.

Came charged out of the box, so far so good, but will know only in the long run.

They really last a lot. Other batteries that I have do not hold charge for a long period.

I am an electrical engineer, and I have tested many, many batteries. The Sony CycleEnery batteries are the best batteries in the world. No other battery has performed as well for me. I highly recommend this battery above all others.

There are two things that make the Sony CycleEnery battery perform so well:

First, if you weigh the Sony battery on a scale, you will find that they are several grams heavier than any of the other brands. This means that there is more material inside, which yields a higher battery life span.

Second, the voltage curve of this battery stays above 1.2 Volts throughout the majority of its life span. The reason this is important is that most electronic devices, such as digital cameras, stop working once the voltage goes below 1.1 Volts. Normal NiMH batteries can have extremely high mAh ratings of 2500 or more -- but you can't actually make use of all those mAh's because the voltage drops below 1.1V relatively early -- this is not the case with the CycleEnergy. Sony has done something to keep the voltage up at 1.2V, so even though the battery is only rated at 2000mAh, they last much, much longer than normal NiMH batteries. I usually get 2-4x the life span out of CycleEnergy batteries, compared to normal NiMH (even the Sony ones!).

To summarize -- these are the best rechargeable batteries on the market right now (2008).

Regards,

~Chris Sebastian

I'm using these batteries with 2400mAh batteries made by Sony. Those last longer than these. I use primarily them in my Garmin GPSmap 60Csx navigator. They last about 20 hours without backlight. With 2400mAh batteries, in same use, it last about 18 hours.
I'm giving 4 stars, because I'm not sure about its life cycle.