alarm draining battery

[ukv6galant]

my uk spec galant has a cobra alarm is this factory fitted or aftermarket?
the reason i ask is over the last 2 weeks when i try to start the engine it wont. after numerous checks i found it to be the battery was faulty.
it was checked under load and one of the cells was caput.
bought a new one and fitted it thinking problem solved but the next day i went to start it i have the same problem.
my alarm has been going off randomly for nothing also over the last few weeks.
so as a test i have been leaving my alarm off.
this solves the problem.
is this a common problem? can i check and fix this myself? or do i need a new alarm fitted.

[littlerick]

the alarm might be going off because of the voltage dropping, it might not be draining it. have you checked if there is anything else draining it?

[fliegendaffe]

the reason why it is going off is because of the battery being low voltage

[ukv6galant]

seems i was wrong with the alarm draining the battery.
i didnt use the alarm last night and when i got up it was lazy starting again. took me 5 attempts to get it to start.
1st turn it flatly refused to start
2nd it started then the revs died
3rd nothing again
4th started so i reved to keep it going but it revved high and low then gave up.
last try it started so i left it a few mins to warm up and its been fine all day???

my knowledge of engines is very limited but a freind said give the air filter a clean so i blew some compressed air over it.
he also suggested some spray he has that evaporates leaving no residue to clean the mass airflow sensor so i tried that.
hopefully this sorts it??
any other things i could check or clean?
i changed the spark plugs 4 months ago for ngk platinum with only 3000 miles done since then.
also when the engine is warm i can switch off the engine and it starts fine.
the problem only occurs after its sat for 10 - 12 hrs.