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Old Honda Civic hatchback 1.4i, manual gear, air conditioning. No longer starting (see below the history).

  • I noticed that with the key off or in the dashboard in position I there is a small 40 mA drain. I am not concerned with that.
  • When the key is in the dashboard in position II (the dashboard lights come up) the battery drain is 10 amperes. With nothing on: no lights, no radio (it's not in), no AC, no brakes, no nothing.

What can drain 10 amps with just the key in the dashboard? (measured with amperometric clamp on the black cable right off the battery with nothing else attached)

Back history:

The battery is old and needs a replacement (it is just dead now) but I used the car for several weeks with the help of a battery charger to keep it from discharging. (it's a Suaoki charger set to SLA, 12V - it stops saying "full").

Last week it did not work and I had to jump start the car with the help of another car's battery (and running engine). It took some 15 minutes, draining more than 15 amps, the car started and I was able to use it, park, restart, park, restart - no problem.

Today I was going to the mall to fetch the new battery (a 45 Ah slim Bosch), but the car is no longer willing to start. Completely dead at first try, seconds after disconnecting the charger, it tries to start when it is connected to the other car running but just can't make it. I then discovered that something is draining 10 amps with just the key in. What can be sucking 120+ Watts?

I am afraid that replacing the battery in these condition will kill the new battery in no time.

I was planning to extract one fuse at the time while checking the drainage to isolate the faulty circuit. Any better troubleshooting idea?

EDIT: fixed grammar and missing piece of sentence (position of key in the dashboard)

EDIT II: After recharging again I was able to jump start the car with another car's battery running. Now I recall that the last time I was alone and did not have anyone pressing on the gas of the other car while starting mine. I guess that, along with the low quality cables I have used (I believe they are aluminum) did not provide enough current and voltage to my car. Now it is running, and while it's running the drainage is only 200 mA.

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    Pulling fuses one at a time is an excellent approach. If the removal of a fuse stops the 10a draw, then something on or connected to that fused circuit is defective. If the 10a draw remains unaffected, then you'll have to look for an unfused circuit (there are often several) or some electrical connections or items added to the car by a previous owner. – DavidSupportsMonica Jan 25 at 17:39
  • Yes, I am going to do that today before I head to the mall to buy the new battery. The way I see it, even if I don't find the culprit, it'll be cheaper to try the new battery - for a few minutes - to see if it fixes things. I am still curious about what is requiring that current with just the key in the dashboard. – Sredni Vashtar Jan 26 at 3:57
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10A at 12V is only 120 Watts. Not much at all and that sounds entirely normal to me just running a few lights and some other electronic devices.

Most auto batteries are in the 50 - 100 Ah capacity range which means that a typical one should be able to supply your 10A load for 5 to 10 hours.

I think you will find that your battery has reached the end of its useful life.

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  • Thanks for the answer. Yes, the battery has definitely kicked the bucket, but... shouldn't I be able to kickstart my car when I am connected to another running car? As for the battery drainage, what concerns me is that nothing was on: no lights, no cigar lighter, no radio, no anti-theft (it's disconnected), no fans, no wipers. Nothing visible. Could be some pump that need to be operated before the engine starts and that keeps draining current because the faulty battery cannot provide the correct amount to perform its action? – Sredni Vashtar Jan 26 at 3:54
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    @SredniVashtar - A quick google on Honda Civic fuel pump amperage finds 'no more than 8 amps if it is running correctly' and yes, the fuel pump would be active if you turned the ignition to the Run position without starting it. Add a few other items like the car's ECU, etc and I can easily see a 10 amp draw. – user16128 Jan 26 at 6:14
  • So, I have yet to get my hands on the new battery (around here it's not easy to find this slim version, it seems - so I've ordered it online) but I finally manage to start the car. Two more recharging cycles with the Suaoki and then jump start attached to another running car. So, it seems that the 10 amps are due to the fuel pump and other ancillary circuits when the key is in position II. I am still puzzled by the fact that the pump seemed to be draining 10 (ok, 8) amps indefinitely, for as long as the key is in position II. What is it doing with about 100W for minutes, possibly hours? – Sredni Vashtar Jan 30 at 16:24
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    Many fuel pumps run continuously when the ignition is on. They provide a constant pressure stream of fuel to the fuel rail in the engine with excess/unused fuel being redirected back to the tank. – jwh20 Jan 30 at 16:27
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    The fuel is pumped from the tank, through a fuel pressure regulator (usually under the hood), and any excess goes through the fuel return line back to the tank. This keeps the fuel rail which feeds the fuel injector(s) fully pressurized at all times. – jwh20 Jan 30 at 16:36

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