One of the downsides of the Nokia E75 design is that the presence of the qwerty keyboard has meant that there's less 'thickness' available for its battery. As a result, Nokia have had to use the 1000mAh BL-4U, with a third less capacity than the 1500mAh BP-4L that normally powers most Eseries phones. Now, it's true that optimisations in S60 3rd Edition Feature Pack 2 mean that the E75 doesn't pull down as much power as, say, an E71 or E90, and that 1000mAh is easily enough to see you through a day of moderately heavy use (especially as you won't be watching much video on the smallish 2.4" screen), but you will have to charge it each night if you don't want to run out halfway through the next day.

If you spend a lot of time on the road or like to go hiking (or similar), away from charging power, then a new option to you is to fit the after-market Mugen 2000mAh battery, purpose built for the E75. As the capacity suggests, this should keep you going for twice as long, and over a week's testing I can verify that this is about right. I went from Wednesday to Saturday on a single charge, with my usual smartphone usage (texting/PIM/music/podcasts/camera/GPS), though I was careful not to waste power outright and didn't keep a data connection active the whole time, for example. I also use 'Offline' mode overnight.

So, with frugal use, I can see this battery giving the E75 a week of operation, which is quite impressive.

The downside, as you can see from the photos, is that the 2000mAh battery is larger. Over twice as thick as the original Nokia battery, which is curious:

Still, Mugen also supply a replacement metal back cover, which hooks into the standard cover latching points. A thicker phone means that you may need a new E75 case - or car cradle. And it means a heavier phone, which may be an issue for you (and the line of your jacket).

The other downside is the cosmetic angle. The replacement cover produces a huge 'bulge', plus the primitive finish isn't as eye-catching as the original textured cover. Now, it's important to emphasise that this is mainly a fashion thing: in the hand, the bulge actually helps use, since the fingers of your hand nestle around it - it makes gripping the E75 easier. But put the phone down or wave it around and the device will look a little 'odd'.

Straight out of the packet, the Mugen battery was fully charged, which is a nice touch. I did have an issue inserting it into the E75 at first, because the battery contacts were so 'new' and stiff. I loosened them slightly with a small screwdriver and then the battery slotted in fine. One other small hardware note was that the replacement back cover didn't fit perfectly - the latches were slightly oversized, meaning that the cover wasn't retained quite as tightly as it should have been. Not a huge problem, but, well, it's very obvious that the E75 has been accessorised!

Only you'll know whether the Mugen 2000mAh battery is right for you - it's a specialist item to be sure, but it does function as advertised and, on a camping trip (for example) might be an investment that saves the day.

Steve Litchfield, All About Symbian, 14 Aug 2009