The batteries are inserted into a carrier, in which they snap with light pressure. Holes on the back facilitate the rapid removal of the dead battery, so that the exchange can be done in under one minute. If the carrier was re-inserted into the housing, wobbles and rattles nothing.
With freshly charged eneloop batteries and C.Fn12 (internal batteries are used only for the electronics and not for flashing) is a flash at full power every second or possible. At constant triggering with 3 frames per second and 1/4 flash output of flash creates 4 trips, then there is a ungeblitztes picture followed by two flashed. This pattern (1: 2) repeats, which I did not try, how long. In practice, this means to me that the flash rate above that of the EX is considerably 580 II without CP-E4.
The number of flashes per battery set is of course dependent on the application. Without CP-E4 I reach in a case about 300 trips with a battery pack, with, I have observed at about 800 trips no fatigue. The stated by another reviewer 1000 - 1200 trips I think is realistic.
Like the EX 580 II is the CP-E4 against dust and splash proof (the latter is a good idea ... at 300V). In the housing there is a hole to the battery pack is to be attached to a tripod socket. The screw this is included.
The (also supplied) bag has a strap and can for example be attached to a belt. It is very convenient that the bag can be opened on both sides: on the one hand, can remove the battery pack, on the other, the batteries can be changed without the CP-E4 unpack.
After so much praise and some criticism: the weight of the camera and lens not increase, I carry the battery pack like in a shirt pocket, or - even better - on your belt. The cable is long enough to, but spans quite strong and bends right behind the bend protection from (at both ends). Here is a slightly longer cable or other structure would be reassuring. Let's see how long it goes well ...
One of my CP-E4 whistles very high frequency while loading the flash capacitor and then rhythmically briefly every few seconds. This points to an inexpensive coil back (again 0.01% of the purchase price in the production saved ...) but above all it sucks mightily.
An indication about the charge status of the batteries is missing. This means that the CP-E4 is in good company with the EX 580 II.
Conclusion: you get here for a relatively large amount of money an accessory that 580 II in certain applications, greatly expanding the capabilities of the EX. If you need these capabilities, it is money well spent, because the CP-E4 works great despite small weaknesses.
