How can I tell if it's aftermarket? I'm not the original owner but I have all the paperwork. It's so odd because I can have my van locked with the alarm system supposedly set but I can still open the doors without it going off. I've been leaving it unlocked the past few days to give everyone a break but feel pretty uncomfortable doing so.
Its hard to say, especially if its a Toyota alarm. I had no idea my Camry was aftermarket until I was told it was never a factory option.
I believe the dealer installed alarms had a switch with a little red light somewhere around the steering wheel. It should say Alarm on it.
If I'm not mistaken, these vans could
be optioned with an alarm from the factory; I vaguely remember seeing it mentioned in the owner's manual. Something about a red light in the center of the dash, on the fuse panel cover I think.
I will check my FSM this afternoon when I get home from work. If I see anything relevant to the alarm I'll scan the pages and upload them for your reference.
I'll have the battery load tested. I've gone through 2 batteries in the past 3 years so this may be an issue
You may want to have the alternator tested as well. It also wouldn't hurt to inspect your battery cables, or outright replace them if they look rough. If the cables look fine, you could replace the terminals.
Batteries should last upwards of 4 years on the lower end, so you've definitely got some kind of electrical problem; though it could just be the alarm drawing too much power.