I bought a HTC desire after a recommendation on here. It’s OK but it doesn’t like hi-cap battery packs and the phone memory has a lot of bloatware so it constantly runs short of space. It connects great with my Sony AS15 via wifi though so any replacement phone will have to do that also.
I’d like to use a HRM soon so it needs to be compatible with the new low power Bluetooth (or something like that). I’m a Strava addict so a smartphone is preferable over a GPS unit.
I’m not ready for a phone upgrade yet so used market is preferred. But if there’s a new device coming soon then let me know!

In summary:
Sturdy Android Smartphone
Takes extended battery
Good wifi performance
HRM compatible

Available for under £150 used

Any ideas?

Some will criticise it as old tech, but I use a Motorola Defy (updated to Android Jellybean via a custom ROM). It is waterproof and compact so suits MTB use. They were going for £60 recently at Three on PAYG for an unlocked handset (I bought another one…), but now all gone… you should get a good used one for around that cost though. Might be worth phoning your local Three store just on the offchance they have one lurking…

Extended battery packs are available, although I have never used one and get a good day of GPS tracking out of the standard battery.