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Discussion Starter · #1 ·
Been having an issue recently with the battery draining itself far too quickly when the cars not in use. Seems sporadic, sometimes it holds a charge fine other times it's gone in days.

It's a new battery that I dropped in the other one had been losing power a bit easy (assume it's the same issue, i.e. problem not with battery).

Only issues I've noticed is that the radio display is now flickery, and I keep finding the boot locked, even when the cars open. Using the unlock button on the key opens it ok, so I don't know if it's just locking itself.

Phantom electronic issues are never fun.

Any ideas, good things to check?

It's an is300 sportcross 2005.
 

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Discussion Starter · #3 ·
Just a couple of days this last time. Let's say around a week, but honestly that's just because of how frequently I've been driving it, it might be draining in a day.

Where's a couple weeks ago it sat for 2 weeks and held its charge fine.

Agree I suspect a short, something that's maybe intermittent. I guess there must be connectors and a ground associated with the boot lock/release - feels like that might be a good place to start looking
 

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Discussion Starter · #9 ·
No, I'm finding the boot to be locked when the car is already unlocked, after having been driving it. There's no way to only lock the boot with the key, and if the key activated the central locking I'd know because all the doors would lock. I don't think this has anything to do with keys, you've latched onto a red herring.

Given the battery drain issue it seems more likely this is some kind of short or ground issue, as I say I just seem to find it locked when the car is unlocked sometimes, something that shouldn't be possible (with any of the keys).
 

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You are just having a parasitic draw overnight that is far higher than usual. In most cars I would say 40-65 mA is about the most you should see when the car is off and parked for the night.

get yourself a DVOM (aka multimeter) that can read amps. 10 amp capability should be ok 20 amp would be better.

Follow the instructions on your meter on how to use the AMP reading function (you normally have to move the red probe to a different slot on the meter) then open the hood and you must start with a fully charged battery. Once it is charged and you know it’s good, turn the car off turn everything off and shut the doors like you would leave it overnight. Make sure nothing is left on.

Now, disconnect the negative battery cable and place one of the leads on the negative battery TERMINAL and place the other lead on the negative battery CABLE you just removed. Your meter should read something now in the form of Amps. If it is above 65mA say like 1, 2 or 3 amps, you definitely have a very high draw.

from here you can start the long boring process of pulling every fuse, one by one and seeing if the amp draw goes to zero or very near zero. When it does, you have found the circuit that is causing the problem and you can then troubleshoot that circuit for a short.
 

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Discussion Starter · #14 · (Edited)
You are just having a parasitic draw overnight that is far higher than usual. In most cars I would say 40-65 mA is about the most you should see when the car is off and parked for the night.

get yourself a DVOM (aka multimeter) that can read amps. 10 amp capability should be ok 20 amp would be better.

Follow the instructions on your meter on how to use the AMP reading function (you normally have to move the red probe to a different slot on the meter) then open the hood and you must start with a fully charged battery. Once it is charged and you know it’s good, turn the car off turn everything off and shut the doors like you would leave it overnight. Make sure nothing is left on.

Now, disconnect the mega battery cable and place one of the leads on the negative battery TERMINAL and place the other lead on the negative battery CABLE you just removed. Your meter should read something now in the form of Amps. If it is above 65mA say like 1, 2 or 3 amps, you definitely have a very high draw.

from here you can start the long boring process of pulling every fuse, one by one and seeing if the amp draw goes to zero or very near zero. When it does, you have found the circuit that is causing the problem and you can then troubleshoot that circuit for a short.
Just wanted to come back and say that this advice helped me find the problem circuit, thank you. I haven't been using my car recently so this was totally put off.

Turns out the Dome fuse had a good 1a going through it. Removing it seems to have knocked out my central locking though so I'm thinking that boot locking issue is indeed related (hopefully not a red herring). Need to double check what runs off the Dome fuse to make sure, there's always a chance I put a fuse back wrong so I don't want to get too carried away ;)

Edit: Definitely has the central locking on it. Now the fun of working out what the actual problem is. That might warrant a separate thread...
 

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Well something sounds like it is shorted somewhere. Does the dome light stay on when all the doors are closed? Trunk light stay on when the trunk is closed?

you can test the door switches individually by opening the doors and pressing them in with your thumb.
 

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Discussion Starter · #16 ·
Dome light seems fine, I didn't think to check the boot light actually I will do that! As I was having that odd issue with the boot locking itself I'm thinking there's a short somewhere on that part of the circuit. I'll try and get to the connectors immediately in that area. Other than a loose connection what kind of thing might I be looking for? Exposed wire I guess but that might become needle in a heystack
 
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