I have an aftermarket alarm system that has drained my battery
Dear Mary. All car alarm systems drain the battery after one week of the car not being used. Also, car batteries are not always fully charged on short trips because to start the engine on each short trip it drains a tremendous amount of power and a short trips do not recharge it fully. Have the car battery checked because the alarm is always on and on standby once installed, they usually have a small back-up battery in the alarm in case of car wires to the alarm have been cut, but that battery is always kept charged by the car battery, so, that is only causing a fraction of car battery discharge. However, to stop it from draining the battery you have to disconnect the alarm, and that is not a good idea. No car alarm that I have known have caused any car battery discharge, but of course if the car is not being used, or it is driven for short periods you are likely to experience a drained battery. Some batteries last more than 5 years not stop while cheaper ones have a lesser life expectancy, but again that depends on a lot of factors, heat from the engine, not enough charge because the alternator has a burnt diode, interior lights left on, too much cranking of the engine to start it and not enough miles done to recharge the battery. Try to get the battery checked and if you do not do any driving for a week, there are a number of solar powered battery charging panels that trickle charge it on sunny days but in winter I suggest you buy a charger that you can connect to the battery to keep it charged. Once charged the charger automatically cuts off and stays on stand-by until the car alarm has discharged it a bit, then the charger sensed the voltage drop and recharges it again, repeating the cycles until you need the car to go out. These small car battery maintenance chargers are inconvenient if you're not using the car too often. Some car alarm with go off when the car battery is disconnected. It's part of the protection the alarm offer. They may not be disconnected from the car battery unless you have a key that shuts off the alarm. But remember, the key shuts off the alarm but it doesn't mean it has disconnected the power from the battery. Check the pilot light status. If it flashes after the alarm key has been turned to off, it means the power is always there. Other alarms remain silent when the car battery has been disconnected from the clamps. If you garage the car at night, you can have a switch installed in the car that switches on the power to the car alarm or you can have the switch connected to a special relay activated Kill Switch that disconnects the battery altogether, but if your car alarm starts to squeal, then you don't need this switch. so try it first, disconnect the car battery and see if the alarm goes off. If not, then the Kill Switch is an option. If it goes off, then there is nothing you can do but to try and have the car battery checked and if you're not driving much or drive short trips, either a solar charger or a Mains powered auto charger can be used to keep the battery trickle charged. But before I go, you say you got an after market car alarm. Looks like it has been wrongly wired, who know. Have it checked by whoever installed it. Good luck.