Does anyone know how much power alarm system, radio & normally on accersories should draw from a car battery?
I have an aftermarker alarm & radio installed in a 3 years old Toyota. When the weather is cold (-15C), the battery is totally dead after sitting for a week. The alarm dealer checked out the current draw & said that 250mA or less (after alarm settles down) is normal; and that the fluid level in the battery seems low. Is 250mA acceptable draw when car is parked?
A steady 250 mA is really a high standby current draw. It WILL run down a good, fully charged car battery in a week. As Jeff points out, that's 42 Ah and that exceeds the capacity of most car batteries. A more realistic standby current draw would be 10 to 25 mA. Go back to your dealer and tell him that he has sold you a defective alarm system and demand that he replace it or give your money back.
No, I didn't. Most car batteries have the capacity to supply 25 A for about hour. That's 100 times the power that the car is using when running. That's a big draw. That's what a car normally uses when the car is on but the charging system isn't charging. But car batteries can supply 0.25 A for over a week without completely draining the battery. So I argued that the power draw on the battery does not explain the dead battery after a week.
Yet all the OP said is that the draw is less than 250 mA. We don't know what the draw is. The problem is much more likely to be the battery than the alarm. A test that the OP can do is disconnect the alarm system next time he plans on letting his car sit for a week, and see if there is a problem starting the car after that.
Go someplace like Sears and they will test your battery and the car. If your car is the problem you could pull the fuse to see if its the alarm. I think Sears charges $5 dollars if you don't buy a battery.
If it helps any starting my Supra is border line at about two weeks with the factory alarm on in warm weather. But doing that is tuff on the alternator and caused damage from battery gasses to the hood over the years!
oh, and I noticed that leaving the headlights on at work until lunch break (4 hours) the battery would still start the car. Whew!
Yep, your right about the current capacity. Of course, 25 amps for 1 hours is 25 Ah. 250 mA over a period of a week is 42 Ah. That's almost twice 25 Ah. You see, the current draw is a cumulative total. A battery that will deliver 25 amps for an hour will deliver 1 amp for
25 hours (25 Ah) or 12.5 amps for 2 hours (25 Ah) but it won't deliver
250 mA for 168 hours (42 Ah). Of course at the end of the 25 Ah draw, the battery won't start the car.
Do you think he picked 250 mA out of thin air? I took his statement to mean that the draw was reasonably close to 250 mA, not 200 mA less than 250. The OP said that the car is 3 years old and we have to assume that the battery is OEM. Most batteries will last much longer than 3 years and, since the cars is almost new, we can assume that the charging system is operating correctly. The battery is still probably around 75 to 80% of capacity.
You are right in that he can take it to some place that sells batteries and they will check it for free. 90% of them will tell him that the battery is bad and sell him a new battery, that's why they test them for free. Then he will have the same problem with his new battery.
You're mistaken. A battery may deliver 25 A for only an hour, but still be able to deliver a smaller current (like 1% of that) for a long time after that. The OP said that battery was completely dead. And he also said it happened with much less than a week, too.
No. But that doesn't mean the draw is near 250 mA.
I took his statement to mean what it said, less than 250 mA. I don't know what the draw is. I am not going to make assumptions.
The tech may have seen that is was less than 250 mA, figured that was within specs, and that it didn't matter how much less.
The 250mA is multimeter reading. When the alarm dealer checked, the current was initially 250mA, then actually dropped to less than 100mA after the alarm settle down. So the dealer says it's not the alarm. I will contact the alarm manufacturer to determine what the actual steady-state draw should be.
The dealer also mentioned that I may be able to top up the battery fluid level as it seems low. It is the original OEM battery.
Mine on my wrangler lasted for about 6 years. But I think the only reason it lasted that long was because I live where it is not that cold in warm california.
If your battery says it is older then 4-5 years old. And you live where it is cold. I would say replace it. You do not want to get stuck with your car in a bad winter storm with a dead battery. Hope this of any help Jamie
You did not mention what kind of Toyota you have. Vehicles with larger engines will usually have larger capacity batteries. 250 mA is on the high side of acceptable for a vehicle with a smaller battery like a Corolla or Yaris/Echo. Car batteries are not designed to be deeply discharged and then recharged like a deep cycle battery is, and the discharge/charge cycles will shorten the battery's life. Jeff and Retired VIP have done some calculations but have not taken into account the effect of the charging cycles over 3 years. Most likely, you will need a new battery because it will not hold a charge like it should, and the combination of aftermarket stuff and a weakened 3 year old battery is making it difficult to start. This is not an uncommon problem with aftermarket security and audio systems. If you disconnect the aftermarket stuff, I'd bet that your replacement battery will last closer to 5 years.
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