Battery NOT replaceable!!!!

A long story...at 4 am this morning I heard a muffled tweeting noise so got up to investigate, to find the smoke alarm sounding off at low volume, in our conservatory...this is one which was supplied gratis by our local fire dept about 9 years ago. Unusual type, in so far as the battery is a high capacity one, reputed to last 7 years...no fire to be seen, thankfully or even a trace of smoke and the annying thing was, no means of shutting down the constant tweet longer than 10 seconds..so I buried the entire unit under some blankets which lay handy and went back to bed. Once morning dawned, I investigated the construction of the thing ,to find it appeared as if a magic wand had been waved over the unit with no means of access to the battery visible at all, so then the fun started, with me levering a screw driver here and there on and between the casing, when I did manage to destroy it sufficiently to cut the visible wiring and silence the shrieking but STILL found the warning light flashing every ten secs...by now I was in full bomb disposal mode and determined to silence this for good...after more levering and cracking the casing apar,t, I found the battery ( The black cylinder in the pic) and cut the terminal wires apart and bingo..the light went out..so I had a ready made Blip on my hands and a visit to buy another smoke alarm during the course of today:)