Having had my Canon 30D for just over a year now I decided it was about time I had extra batteries. The supplied Canon battery seems to last forever and I have never run out of juice whilst on a shoot and even then I have the battery grip fitted so six AA's would get me running again if the worst should happen but they are no substitute for having a couple of spares to hand.

I am normally very brand loyal with my camera equipment and almost everything in my kit bag has a Canon badge on it but £55 for a battery just seems like a lot so it was time for a trip to eBay. A bit of searching around found me a supplier in Hong Kong that would send me two BP-511A equivalent batteries for £8.99 delivered to the UK. I figured even if the batteries were rubbish they were so much cheaper than the Canon branded ones they had to be worth a go.

They were branded with the Phottix name and I had never heard of them, a quick search revealed no reviews of their batteries but some good reviews of their other products so I parted with my money and ordered them. I selected these partly because of the price but mostly because they exactly matched the 7.4 volts of the Canon, some third party batteries were 7.2 and I surmised this would be detrimental to performance. They were however marked as 1600mAh, slightly more than the Canons 1390mAh so they should perform slightly better (on paper).

They arrived quickly so I stuck them into the Canon charger and readied them for some testing.

I placed one of the freshly charged batteries into the battery grip, stuck the camera on a tripod and set my timer remote (TC-80N3) to take ninety-nine shots two seconds apart and hit the start button with the lens IS using juice as well just to simulate real life a bit.

After 200 shots I switched lenses for my 50mm prime as it was getting dark and it is a faster aperture lens. No IS on this one but I left the autofocus on and fired off a further 600 images, to increase the power consumption and more closely approximate real life I also slowed the frequency down to one every ten seconds so that the LCD preview was displayed for about 3 seconds between shots.

To try to replicate a busy days shooting I decided to strain the battery a bit and switched on the on-camera flash to drain it a bit faster. At this point I did speed the process back up to two second intervals so the test didn't take all night so the LCD was no longer draining power. After about 200 photographs with the flash on the battery meter was letting me know the battery was running down. I soldiered on and got another 300 shots with the flash before I thought the recycle time began to slow a bit. I think I may have been wrong...

Turning the flash off again I managed to get a further 400 images from the battery before deciding to reduce the interval again to activate the LCD preview once more. Finally, 2168 images later still, the battery finally died and for those of you not keeping score that means it provided a staggering 3868 shots from a single charge. I don't know about you but that is far more than I was expecting and with both of these in the battery grip I should be able to go away for the best part of a week of shooting and not need to recharge them. I think the most I have ever taken in one day was at an air show where I managed about 800 images.

The CIPA standard testing gave the 30D a 750 shot battery life but I had read of people getting as many as 1400 from the supplied Canon battery but I didn't think I would get anything like as many images as I eventually did.

Through the entire test the shutter didn't start to lag and neither did the autofocus appear to slow down at all so the battery appears to give it's all right up until the end. It remains to be seen how well they perform in real life and how quickly they lose their charge when unused in the camera bag but if this quick test is anything to go by then they are exceptionally good batteries and I would recommend them to anyone thinking of increasing their shooting capacity.