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My car battery drained itself after a week of not being used. I was researching how to identify the cause, and saw a comment under this article saying:

What if I am not detecting a reading but the battery still drains?

You could have a fuse that is draining your battery.

[Not Helpful 5] [Helpful 7]

This sounds like my situation - there's not much drain, but I've had heaps of problems with the fuses (a previous owner "fixed" blown fuses by wrapping copper wire around them, which in one case fell apart inside the fuse box... ugh!)

But I don't understand how a fuse could cause drain like this, or, if I can't measure such drain the normal way, how I could identify that this is the problem and how I could fix it.

Can someone elaborate? What you do if you had a car (97 Toyota RAV4) with no draining electrics, a relatively new battery (six months), high temperature all year, seemed to have a normal level of amp draw when off, but a historically dodgy fusebox and a self-draining battery?

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    The fuse can not drain the battery on its own. Note he's up to 24 "not helpful's" now..
    – agentp
    May 31, 2017 at 20:26

5 Answers 5

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It wouldn't be the fuse which is causing the power drain, but the circuit the fuse is there to protect. (This is the reason why the copied area you have posted has 5 "Not Helpful" votes against it.) The fuse is only a conduit. It transmits electricity. When the circuit transmits too much electricity, the fuse heats up, then "pops", not allowing anymore electricity to flow. The fuse in and of itself cannot be the cause of the power drain. It is, however, an indication of where the power drain is coming from. If by pulling the fuse you get a noticeable drop in battery drain, whatever is causing the drain is on that circuit. It will help you narrow down what exactly is going on.

While batteries do lose power over the long term by just sitting, it should only lose about 5% of its reserve per month ... which in the grand scheme of things isn't a lot. Find the circuit which has the power drain on it, then find what's on that circuit to kill the aggressor.

This post may be of further assistance to you.

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  • Is it possible that, for example, a partially corroded fuse or fuse socket on an always-live circuit could increase drain by increasing resistance? I've had a lot of problems with corrosion, dust, random junk and (recently) damp in the fuse box
    – user56reinstatemonica8
    Jul 29, 2016 at 16:01
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You mention, "no draining electrics," can you say more about how you determined this? It's important because "a self-draining battery" requires something that is causing a load on the battery – especially since you have a relatively new battery.

On newer cars, there is a risk that disconnecting the battery may cause problems with your radio or other on-board electronics. Your car is old enough that I wouldn't be too worried about that. So the first thing that I would do is to measure the drain of the whole car by disconnecting the ground terminal from the battery and then measuring the total drain with an ammeter between the ground (negative) terminal on the battery and the cable you disconnected. The drain should be a few tens of milliamps at most. Much more than 50 mA and you should start looking for drains in the electrical system. You can do this by pulling each fuse in turn – the one that causes the load to drop is the culprit, keep going until you are down under 50 mA.

Some things to check that could cause a battery to drain, even when you don't see obvious loads after checking with the fuses:

  1. Is the battery getting charged fully. With the engine off the battery should be 12.6 V or even a bit more. With the engine running the voltage should be higher – maybe not much higher at idle, but if you bring the engine up to a normal cruise RPM, say 2,000 or so, you should see something between 13.5 V to 14.5 V (a bit more or less isn't necessarily a problem).

  2. Is the top of the battery clean? Dirt, especially damp, conductive road dirt can drain a battery without an obvious load. To test for this all you need to do is to clean well around one terminal – you just need to break the circuit.

  3. Does the car have a history of leaks or other water damage? Water usually contains dissolved minerals so leaks around fuse blocks or relay panels may create high-resistance shorts that won't blow a fuse but that will add a small drain. If the water deposits are "before" the fuses you won't see a problem if you check for drains by substituting a meter for each fuse in turn.

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  • Dirt and damp sounds likely, we've just entered the rainy season here so humidity is high and the engine hasn't been cleaned for a while - can you elaborate a little more on "To test for this all you need to do is to clean well around one terminal" - how would I identify if this was the cause? Presumably any damp dirt would be cause for suspicion?
    – user56reinstatemonica8
    Jul 17, 2016 at 13:40
  • I'd be suspicious of anything that looked like it was damp. Older batteries could vent some acid and the top could be quite conductive. You might use some baking soda to help clean. But don't let it get into the battery. If you clean around one terminal and use a meter to measure current between the clean terminal and the dirty area on the top of the battery you might be able to see if that was the problem.
    – dlu
    Jul 17, 2016 at 14:04
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    Just to be totally clear, you do not want to try to read current between the poles of the battery. That would be a direct short and you'd blow the fuse in your meter or destroy the meter (if there isn't a fuse, or if the fuse doesn't blow fast enough).
    – dlu
    Jul 17, 2016 at 17:18
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    That's precisely the age of car that's given me trouble with radio codes etc. in the past, so be careful
    – Chris H
    Jul 18, 2016 at 8:36
  • That's good to know. One way to be careful is to use your meter leads or a small jumper cable between the battery negative (ground) post and the ground cable – this puts the meter or jumper in parallel with the ground connection so that when you remove the cable there is still a connection. If you use a jumper, once you get everything squared away you can hook up your meter and then remove the jumper. It can take a bit of juggling to get it set up, but it's not that hard. Really :-)
    – dlu
    Jul 18, 2016 at 14:29
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What can drain your battery is Alarm system, Radio (memory), Remote control key (radio signal receiver), ECU, Clock... Can't imagine anything else. Even if you have all of this, they shouldn't drain a battery in one week.

Only thing you can do is to get a Ampere Meter and stick it in that faulty fuse to see what it drains. The fuse can not drain anything, it must be the wires or the device that the fuse is for. Find out what the fuse is for and let us know please..

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I had a daily battery drain. Had to recharge battery nightly just to get to work the next day .. After a week of this..I bought a new battery as the other would no longer charge to full capacity. Then I checked the fuses under bonnet & under dashboard. I found 1 open fuse for the internal light which I replaced ..and 3 fuses in places where it was meant to be empty .. not in the spaces where the spare fuses go, but in places the diagram showed were meant to be empty. I removed these 3 fuses .. and lo and behold .. no more battery drain..it's been 4 days now and it's all good. I haven't even driven the car for 18 hours .. but I just went out to check by starting her up and she goes...God bless her little engine... she goes...

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  1. Replace those fuses by proper ones, they are inexpensive. Then test your car to make sure everything still works, then inspect the fuses again.
  2. Some aftermarket remote starters will drain your battery very quickly. My dad's 96 Toyota Corolla had this issue, it stopped when we disconnected the remote starter.
  3. Test your alternator, make sure your battery is getting fully charged.
  4. Clean your battery terminals and inspect your battery cables.
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