From time to time I shoot the odd event/function and occasionally during these events I might get cause to do a bit of flash work. It's normally fine until the batteries are wearing a bit and the flash fails to recharge before the next shot. I could carry more batteries, but I'd rather not keep changing them. So the solution for many is a battery pack. Often the cheaper option is to opt for a AA cell powered device. If I made my living using flash I'd probably opt for a Quantum or similar. Being a cheapskate I like bargains, but I also prefer original equipment (excluding batteries). So I have a couple of original options for my Canon Speedlites: 2nd Hand CP-E2/3 between £60 - £100 if you can find one. Canon CP-E4 at around £150 Either way it can't compete with an Ebay price of £21 for a clone of the EP-N4. Anyway on with a mini review. The device itself does everything you'd want from a small compact device. It provides additional power for a compatible speedlite (550/580/580mkII/MR-14/MT-24). The refresh speed of the flash does depend on the flash power, at 1/1 power ratio you will still need to wait for flash to charge for the next shot, but it will be much faster to refresh compared to the internal batteries. Build of compatible devices is always a little bit of a worry. Just looking at the device you can tell it's not a quality piece of work, the plastic looks cheaper and finish on some edges isn't great. In fact the battery cage needed a little trimming to fit better once the batteries were installed. To add to battery pack woes once inserted in to the device it requires a squeeze to slide the end clip in. Once it's lined up and in place it holds fine. So on the face it good at what it does, but cheap build. To be honest I have no issue with that. It cost £21 including shipping (From the UK) and arrived in 2 days. Looking closer at the product I've noticed the weather sealed plug and battery flap. However the instructions indicate it's not water proof - so I guess using it in a pond is out then. Seriously though, my Eos 5d isn't water proof either and I'm perfectly happy to use it in light rain. Same applies to this pack. Most times when used it's likely to be in the supplied pouch and attached to my belt. Once fitted into the supplied carry case it's easy to slip into a jacket pocket or put on your belt. You only really notice you have it once you install the 8 AA batteries. So overall - Cheap product, cheap build, cheap price. With the predicted use this is going to get it should last a while. Maybe for those that are professional it may not take the wear and tear that a Canon branded device may take. Weather Sealed Plug? DIY trimming Size comparison with the original Canon CP-E2 Case, also comes with a screw to attach to the tripod thread on the camera. Caveat: People are wary of 3rd power sources - often scare stories from Camera shops will tell tale of exploding batteries/damaged cameras etc. I can understand that, I note that this device is CE certified so that may provide some reassurance - I make no guarantee that this product wont damage anything. Though if they did I'm fairly sure we would have heard more about it. Also if you go down the Ebay route to purchase be aware that many different brands are available, often shipping from China/Hongkong - so you may be liable for import duty etc.