I got one of these so I could move my Pure Flow around without having to unplug and plugin again every time.
For this it works as expected and I'd no problems fitting the battery.
I've only used it for short spells on battery but did try to run it for a few days on battery only as a test. I didn't measure exactly but it gave about 15 hours of use mainly DAB radio (I like to listen to Planet Rock while working at home !) but with a couple of hours streaming also.
I don't think it says anywhere in the specifications when buying but for the technical it is a 3.7v Li-ion 8800mAh battery.
And now to the limitations which I'm not sure are documented for the Pure Flow for when you have the battery installed -
- if you have the Flow on standby and unplug it, it switches off completely and then reboots when you switch on.
- if you unplug from the mains while it is switched on it stays on and the battery takes over.
- you can't set the alarm when running on battery only but it does give you a message to say this if you do try.
- so you can't use as an alarm clock on battery power only, it must be plugged into the mains
- the 'on' button seems to need to be pressed for a little longer to switch on than when running on mains. At first I thought the battery wasn't working until I did this.
None of these actually bother me but I've seen some comments in the forums about this, so be aware.
I've given 4 stars because I still think it's a little pricey, but then again I've just looked at camcorder batteries which are about £12 for 1400ah or 2000mAh so I suppose about £27 for a 8800ah battery is in proportion.