Battery problem?

[skydriller]

Hi all,

Mine's a 2004 Porsche 996 C4S Cabrio, owned 2 1/2years...

First a little history :

I have a CTEK plug in maintainer that I have had a year or so (since once returning to a dead car after a 4 week trip away!!) and it plugs into the cigar lighter when the car is in the garage. Have had no problems with this arrangement until about a month or two ago. Came home once again from a 3 week trip and started the car no issues, but having driven it for 10mins or so, left it for 30 minutes and it then again wouldnt start...jump-lead started it and since then have used the CTEK and its started OK as before...

Then Yesterday, returned from a 20minute blast, and wanted to go out next day, so didnt plug it in, and once again had a problem starting it - she turned over once, then clicking!! - plugged in the CTEK for an hour and she started no problem once more....went for another quick blast and on returning again she wouldnt start after leaving standing a couple of hours. This time plugging in the CTEK didnt help and I needed to jump-lead start it to be able to move it off the drive and into the garage...

Now Voltmeter on the battery terminals shows 14V with engine running, then initially ~12V (decreasing slowly) engine off, but after a couple of hours voltage appears to have dropped to 10.4V and several hours later is still at 10.4V....This probably explains why I get a single turn over, but no start...

So, is the Battery dead, or could it be something more sinister??
Is there anything else I should be checking for a diagnosis??

Any advice or pointers gratefully received,

Regards, SD..