Dead battery?
 

My 2003 Outlander Sport SE would not start yesterday, completely dead. I removed the battery suspecting it to be flat and charged. When I replaced it, I could hear a clicking sound but engine would not turn over. I did wonder if it might be something to do with immobiliser/alarm system as central locking on key fob doesn’t work and nor does imobilizer button. I replaced batteries in key fob but still no luck. Also, when I unlock car manually now, alarm goes off and won’t stop until car locked manually again. Is this just a case of needing a new battery or does anyone think there might be another cause? Thanks in advance.