TribbleTrickswithTinsel - If you check the specification of any phone on GSMArena, it should indicate whether the battery is removable (but there are some battery packs which might be worth considering - I paid a tenner the other day for one on Amazon from Anker - about the size of a lipstick - and have seen others at up to 20 quid with considerably larger charge capacity).
Ten or 20 quid is not too expensive and can be used with multiple phones over time, whereas a replacement phone battery is only good for phone(s) from one manufacturer (I have a number of different batteries from one manufacturer, for their different phones, from days before the micro-USB plug became very popular as a 'standard').
As far as mobile phones go, I'd throw in the Motorola Moto G (around 150 quid) as something to look at - there are 3 or 4 models now, depending on whether you want 3G or 4G, and a single SIM or dual SIM. The original (2013) model is only 3G and has a 5 MPixel camera (where the 2014 model has 8 MPixel) but can be 8 or 16 GB, 2014 model has only 8 GB for films, music, photos.
Of course I was looking for someone else on the 'Which smartphone to buy?' thread. Since you've got an iPhone 5, then your monthly charge may be quite hefty. There are two higher spec Motorola phones, the HTC One M8 and so on to consider (check that thread, I don't know the size/weight of the iPhone 5 but I was comparing phones with 4.5" to 5.5" screens).
You may consider the very latest Google Nexus 6 phone, made by Motorola, a big sister to the Motorola Moto X. Some of the latest phones use different (no wiring, just a portion of your mousemat, perhaps) methods of recharging, such as by induction loop.