Battery problem?
 

Lately I have been having problems with my battery running down after leaving the car idle for 4 or 5 days.
The nearly new battery has tested good and the nearly new alternator has tested good.
So I decided to do a parasitic draw test. I had a draw of 2.6 to 3 amps. which turned out to be the radio/cd unit.
Anyone know if this is normal? The radio does have a small flashing led but not sure if this is the draw.
I also did an overnight battery test. I disconnected it, it tested 12.4v at 8pm and the next morning at 8am it was 12.0v. I'm not sure if that is a normal drop for 12 hours.

Any ideas appreciated.

2.6 - 3a is way high. Your battery probably has 120aH of capacity so in about 40hrs, you'll have a dead battery

Start unplugging stuff... I would start with the easy stuff - disconnect cd changer, check current draw, then move on to the amp (assuming you have the factory amp)

Check the stereo to make sure that the memory and power wires aren't reversed.

That is not a normal overnight drop. The 24 hours drop should be almost unmeasurable.

And the starting point should be in the 12.6 to 12.8 (conventional - AGM) range

The draw on the battery in circuit after 60 some minutes should be 30/1000 of an amp.

You have checked the grounding strap and all the connections I suppose. Measured the charging voltage at 3k RPM.

I turned off the flashing LED of the radio (thru the settings). There's really no need for it.

[QUOTE=mikefocke;522996]That is not a normal overnight drop. The 24 hours drop should be almost unmeasurable.

That drop was the battery disconnected - I am starting to think my battery may be the problem. I have charged it for 7 hours and it is at 12.4v. It never seems to get any higher.

I'm gonna try and charge it up (disconnected from car) to 12.6 and leave it overnight again to see if it drops again.

If the battery voltage is only 12.4v maximum after a 7 hour charge, then the battery is faulty.
As Mike indicated, 12.6v is the norm for a fully charged battery, while 12.4v is a ~70% charge.

Just to check that i am using my new multimeter correctly I'm enclosing 2 pics of how I set it up and the reading - it fluctuates between 0.25 and 0.1.
If I do not have it on the correct setting please let me know.

Thanks for all the help.http://986forum.com/forums/uploads02...1484604887.jpg
http://986forum.com/forums/uploads02...1484604898.jpg

You need to be more precise. Read the specs. The draw on the battery after you turn the car off will change over time as the systems take their time shutting down and eventually go into sleep mode. Someone may have those specs or Search.

[QUOTE=njbray;523006] Sorry I wasn't clear. The 24 hours disconnected drop on the battery should be to no lower than 12.8 for a normal battery and 12.6 for AGM.

I presume you can get to a battery shop which should be able to both test the alternator output voltage and load test the battery. Or even just take the battery fully charged to the shop out of the car.

If not, buy or borrow a load testing battery tester.

Ah the problem with written communication, You can't tell when the person doesn't understand and you have to wait for a written query when a furrowed brow would have given you the clue.

Sure we do here.

Looks like you need a new battery. Get the bigger option for your Box if you have the regular sized battery.

I just fought something like this on an eleven month old battery. Solved a few different issues once a new one was installed.

How would a bigger battery be better - in Santa Barabara? In a cold area ,perhaps.

Check out https://www.batteriesplus.com Stores in many areas around the US....You can locate a store nearest you using your zip code on the site....

Why not? More Amps, more of everything a battery does. More weight too :-( . But more battery is probably better.

Larger battery is typically for auto trans cars, in the 986's case, a TIP.

In a mild climate like the OP has, there is no advantage to an oversize battery.
Hence the choice made by Porsche. An oversize battery is just more expensive and more weight - two things an engineer tries to avoid.It is different in a cold climate - hence the space for a larger battery.
For local reference a 700cca battery(regular size/capacity for a Boxster) easily starts my 6 Liter Cummins turbo diesel on the coldest days in S.California. It uses the same size as the Boxster. And that is one heluva lot more compression and mass to rotate and power glow plugs and a pre-heater - compared to an M96

Yup. To be specific the specification is a 94R (TIP) vs a 48R(manual trans).

UPDATE:
Sooo... I charged up battery yesterday (still in car but disconnected) to 12.8 at 4pm Monday. Just tested it at 12 midday today and it is 12.1
Makes me thinK it's a dud cell.
I think it's back to Costco to replace with another Interstate 700cca battery.

The car could be in Devon, UK...