Nissan qashqai j10 alarm keeps going off

[Tuffs]

Hi my nissan Qashqai j10 2013 alarm keeps going off I have disconnected the inside sensors by the lights,I have took off the bonnet switch and joined wires but as soon as I have reconnected the earth on the battery it just goes off,than 30 seconds later does it again if I take off the earth it carries on for a couple of minutes but than suddenly stops, the car batteryis fine and fob battery has been changed,is it a case of a new alarm battery,I know its at the back passenger side,does anyone have any information on how to replace/buy it please as its got nothing in my hanyes manual, the car will still start and run well the alarm is going off,central locking still works well its going off but the fob dosnt stop the alarm,tia