I have one of Smudge's unit too, it great and you can rely on Mark for backup. The XML compared to my old P7, it's the next step up, a brighter beam with more punch/throw than the P7 managed. Though in with a tighter beam has less overall spread than the P7, Maybe the (current) ultimate in helmet lights.
BUT as you have a budget of £100, I would definitely be looking at the MJ-872 and Neninja Inton units. The XML still has more punch/throw than the MJ-872 but not the massive flood of light the later produces. M8 has just got hold of a Neninja's unit, we hope to compare it with a MJ-872 tomorrow night, to see if the extra cash was worth it. Off-hnad a quick back garden test of the Inton U2, it has a massive central spot, which was bright as f***, and a huge secondary halo. Whether like the single XML this secondary halo is overwrought by the centre spot, we'll see tomorrow
(all dependant on my cold shifting or at least not getting worse)
Or you could simply replace your P7 battery (I assume the reason it died, or at worst pull the head unit apart to locate the fault), and run a 2nd XML unit along with it, as between them you'd get loads of light.