Battery is recommended every 4 years, however as you rightly note the loft is a piss poor place to fit the panel (thousands are fitted in them though) but the extremities cause premature wear so I'd arrange a new battery whilst you are up there. The battery wont be the cause as the unit is dialing but I'd check voltages and loads in alarm both at the speech jobby and phone lines. The unit itself sounds like it's goosed and the only thing the speech and mic have in common would be the processor so probs not worth fixing.