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8th Gen parasitic battery drain

paultop6

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Hi,

So my Type S has developed another issue, this time its a battery drain.

Bsaically the battery is being emptied if I leave it for a few days without usage, or across 7 or 8 days with light driving (maybe 15-20 miles per day)

Not much aux draw on the battery when driving as it is summer (I havnt had A/C on or anything like that, and no headlights as havnt been driving at night)

Im gonna do the old pull the fuses test and see where it is comming from hopefully.

I just wanted to ask if there where any known issues with the 8th gens when they get on a bit (mines 2009) around battery drain.

Just to point out the battery isnt the issue, it is brand new (~few months). I replaced the previous battery thinking it was the issue for the non-starting, but it is deffo a parasitic drain
 

Bounder

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I know the 7th Gen had issues with the HFT but I haven't heard of any with the 8th Gen HFT, it could be the HFT module but the only way you will be able to pinpoint it would be to use a multimeter and go through the fuse box to see which fuses are still carrying current when switched off.
 

paultop6

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I have had the HFT module disconnected and the issue persists so thats not the issue.

I was doing an initial test to see what the amp draw was when the car was asleep. If it was a bad parasitic draw it would show up there.

With all doors closed, I placed the multimeter in series between the neg terminal and ground.

When everything was asleep, the drain was only 0.01a, which is nowhere near enough to drain a battery in a few days.

So, the next test I did was to see how hard a time the battery had under load.

With no load, engine not running im getting 12.4/12.5v which should be healthy for the battery.
With engine running, no adverse load, im getting 14v
With as much load as I can muster (headlights, heated rear window, heated seats, heated wing mirrors, fog lights, radio turned up) it droped to 11.9v

11.9v seems a bit low under load.

Now, the interesting part was the car started fine before the load test. But after the test the car wouldnt start again. However the battery voltage still read 12.4v which meant it was still charged.

Does anyone have any ideas here. Seems like very odd behaviour.
 

paultop6

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I have just realised that the replacement battery I got for the car is of lower capacity, 52ah vs 72ah

Also, the new batter Cold Crank Amperage is 500 vs 720 of the OEM batter.

Could this be enough to cause an issue?
 

Channel Hopper

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Boot or glove compartment light remains on ?

Are there any devices still connected to the accessory sockets in your car ?

I only discovered yet another charging point in the tourer (under the centre console armrest) a few weeks after getting the car.
Has one of your passengers fitted a USB charging unit somewhere without you knowing ?
 

Bounder

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I would start looking at the alternator output, it might be fine at low loads but break down under high demand.
 
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