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SRDavis
Newbie


Joined: 08 Jun 2015
Posts: 20
Location: Carmarthenshire


PostPosted: Sun Dec 01, 2019 8:26 pm    Post subject: Flat battery; causes? Reply with quote

After not using the car for 2 weeks, the battery was as flat as a pancake. I've read many posts about how to use a second battery to start the car and lots of debates about makes of batteries and chargers, but haven't found anything that says why 997 batteries go flat.
I have a circuit tester but not much expertise with vehicle electrics, so can anyone tell me, (as in giving facts, not hearsay / opinion), as to what are the typical causes of battery drain on our cars?

Thanks

Simon
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deMort
Dijon


Joined: 21 Mar 2015
Posts: 7573
Location: Brighton


PostPosted: Sun Dec 01, 2019 9:02 pm    Post subject: Reply with quote

An interesting question .. the reasons ...

Lack of use .. the battery will always have a discharge but it's in the 30 milliamps range .. so approx 5-6 weeks for a new fully charged battery to get to 9 Volts .. ish so that there is not enough power to spin the starter fast enough .

less for an old battery .

As above but short journeys .. more out of the battery than in .

A poor performing alternator .. you may not get a battery light but you can get a low voltage from the alternator .. to test you always have the engine running and all electrical loads turned on .. ie lights , seats , blower fan at max ..

You want at least 13 volts at this point .

An electrical discharge .. something drawing a current .. a Tracker is a possible .. roughly a 1 amp intermittent discharge every 30 seconds .

Constant 1 amp and its a radio or an alternator fault .

Pulsing 6 amp and its stuck seat button .. i could go on here ...

An old tired battery that cant hold its charge .

Those are the obvious reasons and you always test with a seperate voltmeter .
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NLW73
Albert Park


Joined: 27 May 2014
Posts: 1553
Location: Yateley


PostPosted: Mon Dec 02, 2019 8:07 am    Post subject: Reply with quote

cold weather and lack of use.

if your battery is a few years old and you don't use it then this recent drop in temps will just kill it. especially when it goes sub zero. same with a normal phone when you are out in low temps. battery life just drops

when you are asking it to crank a big lump then its like no thanks. plus all the electrics running in this weather such as heating and lights and heated seats etc.
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timbo1811
Silverstone


Joined: 13 Dec 2016
Posts: 129
Location: Dorset


PostPosted: Mon Dec 02, 2019 10:01 am    Post subject: Reply with quote

The alarm uses a bit, if you are in a position where you dont need to lock it it will last longer.
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chunkymonkey1982
Newbie


Joined: 19 Jun 2017
Posts: 23



PostPosted: Mon Dec 02, 2019 10:23 am    Post subject: Reply with quote

I’ve read up on this too. I had the same issue a few months back. What I found out was that my battery was 3 years old, and was a genuine Porsche one which I understand are not the best battery. My car also has a tracker that drained the battery. Replaced with a Bosch equivalent, no issues. Had not used the car for 2 weeks and started no issues yesterday.
 
  
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C4Silver
Spa-Francorchamps


Joined: 14 Aug 2019
Posts: 272



PostPosted: Mon Dec 02, 2019 10:37 am    Post subject: Reply with quote

At this time of year the number 1 contributing factor to a car battery health is Weather,

The battery may well be tired and old, the Alarm will drain some a tracker will also drain but the weather will highlight any issues pretty sharpish especially the past few nights of sub zero temps we have had around here.

Another effect that i think often gets over looked, the battery is away from the engine compartment and doesent have the benefit of being kept warm for a few hours after the car is parked up,
 
  
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Hertsdriver
Nürburgring


Joined: 12 Nov 2018
Posts: 468
Location: Hertfordshire/London

2004 Porsche 997 Carrera 2

PostPosted: Mon Dec 02, 2019 11:04 am    Post subject: Reply with quote

C4Silver wrote:
At this time of year the number 1 contributing factor to a car battery health is Weather,

The battery may well be tired and old, the Alarm will drain some a tracker will also drain but the weather will highlight any issues pretty sharpish especially the past few nights of sub zero temps we have had around here.

Another effect that i think often gets over looked, the battery is away from the engine compartment and doesent have the benefit of being kept warm for a few hours after the car is parked up,


This /\/\/\
A 911 battery is always more likely to go flat, the cable run from front to back is a power sapper, and as said above it is physically colder than a battery stored in an engine compartment (im sure this is a good thing in a hot country...)
I also think the standard battery is an engineering compromise of power to weight, whereas on a bog standard hatchback an additional half a kilo doesnt matter, so a battery will be slightly larger and therefore have a better capacity than is required, a 911 battery is right on the edge and therefore has to be kept in top condition. Thats only a theory though Floor
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C4Silver
Spa-Francorchamps


Joined: 14 Aug 2019
Posts: 272



PostPosted: Mon Dec 02, 2019 11:41 pm    Post subject: Reply with quote

Floor

As theories go it’s about as un scientific as mine...... it’s just one of those things that works in my head when I think 💡

If the engine bay was keeping the battery warm it would stay in better condition......
I know a lot of More modern cars have the battery in the rear floor under the boot floor, I have a car with a battery in the wheel well, it’s about twice as big as the 911 battery.
 
  
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-- 997 --
Barcelona


Joined: 11 Jun 2015
Posts: 1270



PostPosted: Tue Dec 03, 2019 2:09 pm    Post subject: Reply with quote

When my car is locked up and i dont use it a while i disconnect the battery! Even now in winter its all disconnected!! Safer in my opinion!

Cheers

J
 
  
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deMort
Dijon


Joined: 21 Mar 2015
Posts: 7573
Location: Brighton


PostPosted: Tue Dec 03, 2019 7:27 pm    Post subject: Reply with quote

If your going to leave a bonnet open then its always best to drop the latch ..

By this i mean ...

use a screwdriver flat blade .. push the lock down a small amount and you will see a bar start to move from the o/s to the n/s ..

Put the screwdriver behind this and move it towards the n/s whilst pushing down a bit .

You are doing what the bar in the bonnet does basically .

Latch locked and there is no way it can be shut accidentally .. you can also alarm the car should you wish if not disconnecting the battery .


Something i do many times per day to turn off the bonnet interior light .
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