I was going to upload a screenshot of my battery drain, but it seems it only accepts URLs and I cant be bothered to upload it somewhere and get the link...
The low down on battery is that I get good daily usage from it. Current stats are: 13h 51m on battery and I have 42% remaining. This is from being connected to 4G all day, made a few calls, lots of texts and Whatsapp, facebook, twitter and Glassboard usage, I also used the Mini as a hotspot for an hour this morning, have used to phone to demonstrate this handset and Android to customers and played a couple of short Youtube videos. I probably get the same battery life from daily use as I did when I had the full sized One. I guess the smaller battery is offset by slower processor, smaller screen etc. In the week I have been using the Mini I have not ran out of power. The lowest it's been was on day one when it fell to 6% - but it didn't come fully charged and I was busy installing apps and getting set up.
Signal quality - I haven't really been out of the city centre (Bristol, UK) since I got the phone so I don't know how good the phone handles lower signal strengths. One thing that I have noticed with the Mini and I saw the same with the full sized version is that if I have the HTC One mini and my Lumia 920 next to each other, the Mini often displays lower signal strength than the 920. For example - right now the lumia has 3 bars of 4G and the Mini has 2 bars, I've just run speed tests on both (using Ookla SpeedTest.Net apps on both) simultaneously and the results were:
Mini: download 29.4mb/s upload 10.9mb/s
920: download 28.1mb/s upload 13.8mb/s
They are always pretty much the same on speeds, it just seems that android/htc interprets signal strength differently. The One Mini switches from 4G to 3G and back for calls and texts nice and quick. Not had any problems with network signal - but like I said I've not been to a low signal area to test fully.
Other things I've noticed over the last week:
The speakers really are great, it's so loud, I wasn't ready to believe that this little phone could be as powerfully loud as the HTC One, but it's almost as good - speakers on the front of phones should really be the norm!
The camera is OK, its perfectly fine for point and shoot pictures - I do miss the extra ability of great looking night photos and smooth videos that come with the Lumia 920 and the One, but I guess I've been spoiled over the last few months with the benefits of Optical Image Stabilisation.
Still loving the build quality, anyone who is trying to decide whether to get the HTC One Mini or the S4 Mini should wait until they're in shops and then just hold one in each hand. The feel of difference in quality is astonishing, the HTC wins hands down here - Hell even if you're wondering whether to get the full sized versions of these phones hold both of those and feel how nice the HTC is.
So this isn't all one sided towards HTC where I think Samsung wins is the screens. I don't know what it is but the S4 and S4 Mini screens just seem more vibrant, more colourful. This might just be my perception, but the screens on the HTC phones seem to lack bright colour, every thing seems a bit grey - not overly so that you'd notice or care, but I just feel noticeable when you hold both HTC phones next to the 2 Samsung models.
Hope this helps with your decisions people, if you have any other questions and ask away, I pop here every now and again to check