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    Thread: Normal current draw when a car is turned off ??

    1. Member Merc-MarkO's Avatar
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      03-08-2011 06:44 PM #1
      As the title says.

      I sometimes don't drive my Mazda3 for 2 or even 3 days and I've noticed over the past couple of months a hesitation in starting after those 2 or 3 days. I put it down to the battery having a hard time due to the number of short trips I do and maybe not charging all the way.

      It's in the shop right now for a recall (steering pump) and oil change and when they were doing their usual general inspection, they noticed a small draw on the battery when the car is off. They didn't say how much current is being drawn (I can ask later) but the car is stock* so I'm unsure what the root cause could be.

      What would the normal current draw be ?? 50mA ? More ? Less ?

      * 3yrs ago, I swapped a single cd player for a 6cd unit out of another 3.
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    2. Member mraguilar's Avatar
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      03-08-2011 06:47 PM #2
      Id say between 500mA ~ 1A, just a guess out of my ass

    3. Banned justanotherusername's Avatar
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      03-08-2011 06:55 PM #3
      Quote Originally Posted by mraguilar View Post
      Id say between 500mA ~ 1A, just a guess out of my ass
      That's probably on the high side. A typical dome light is 12w, which would be a 1 amp draw, and that will kill a battery over night.

      I'd guess more like 250mA max, with most vehicles being under 100mA. Really the only things being powered when the car is off are the keyless entry system, and the clock memory. Both those things combined would be under 20mA.

    4. Member Live-Wire's Avatar
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      03-08-2011 07:03 PM #4
      Quote Originally Posted by mraguilar View Post
      Id say between 500mA ~ 1A, just a guess out of my ass
      That seems a little high (1A). Your battery would be dead in 3 days to a bit over a week.

      It really depends on the car, an Audi A8 might be upwards of 1A. A 'normal' car would be in the low 100's of mA range. You should be able to not use it for over a week and still have it start up fine.

      You'd need to talk to the engineering rep for the car maker - and get the real answer. Our guesses are as good as yours. If you have an alarm system or remote starter your draw might be higher then recommended.

      Short trips are harmful to the battery. You have probably shortened it life and maximum capacity... which is why you are noticing the car is having a harder time to start. I'd guess if you got a new battery it would be good for another while.

    5. Forum Sponsor Brendan@bwalkauto's Avatar
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      03-08-2011 08:00 PM #5
      My friend who works on Ferrari's says that some of them have a >500mA drain, and will die in a few days if not on the tender. Elises have a >250mA drain, and we either disconnect the batteries or put them on the tender weekly, other wise by day 7 their tiny little batteries are done.

      I'd say most normal cars are in the realm of 100mA, but I have nothing of value to back that up with other than this bag of anecdotal evidence.
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    6. Member redsoxreturns's Avatar
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      03-08-2011 08:32 PM #6
      8-10 mA is considered "spec" on most Saabs after 12-15 minutes. I'd say under 50 mA on most cars is what you're looking for.
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