I'm still running my HTC Desire S - with the original two year contract now long since paid off, I'm hoping to wring a few more years out of it on pay as you go.
HTC have finally released an Android 4.0 update which has made the phone a lot more usable (mostly by allowing more modern apps to work), but battery life has been getting worse and worse, culminating in my being stranded in the middle of Wandsworth in the dark with no phone to navigate or call for help with and no idea where I was.
I was a little dubious about putting third-party batteries in the phone - even if they were slightly higher capacity than the increasingly worn out original, how good could they be at two for £14?
In fact, they're excellent - my phone now has the battery life to survive a heavy day's use on a trip to London, and if the worst comes to the worst, I have a spare battery I can swap in. The inclusion of the charging dock is a neat touch, so you can plug in a USB cable and charge the other battery when it's out of the phone. The battery indicator in the status bar seems to be calibrated to the capacity of HTC's original - on the new battery, it remains at 100% for several hours of light use before decreasing.