New Battery?

Hi all, I have read posts about similar-ish problems relating to battery problems in the past, but just in case wanted to share this before getting a new battery. I have a 996TT which is only driven on weekends with motorway/dual carriageway journeys which last 2-3 hours every weekend. Normally if the car isn't driven for 5+ days it goes into shutdown mode and when it is started you expect a little extra effort (at least I do) to start. This week I have been driving it to work and having not driven the car for 3 days, when starting it was as if I hadn't driven it for a few weeks, car started with the windows twitching down and back up, and the dash computer resetting the settings (except main mileage unfortunately!). Car runs fine once started and no problems. Looking for a second opinion of experience to confirm this sounds like a routine need to change the battery rather than anything more. Appreciate any replies.

How old is it? On both my 996's, I have had to replace the battery at around 4-5yrs old and I do similar driving to you ie all week in the garage and a blast at the weekend

Probably not this... But check the carpet under the passenger seat isn't wet (front back & sides). Just in case some rain has crept in through a blocked drain or broken door seal, and made the control unit under the seat a bit damp. (If it has, get the cause fixed asap - or it gets expensive! )

Could be the battery on its way out, but it could be many things. You really need to put a meter across the battery and check its reading around 14V with the engine running. Then check the battery with the engine off - it should read around 12.3V initially and with a heavy consumer like headlights on will only drop away slowly, if it falls to 11V or less within 30 seconds or so then its probably on its way out. If you don't see at least 13.5V at the battery with the engine running then your alternator may be failing - you can replace just the diode packs on these (its a simple plug in module) rather than replacing the whole lot. Dependent upon what battery you have you may be able to remove the cell covers and look inside for electrolyte level and cell condition. IF you are not using a trickle charger between the car being driven then its another way to kill the battery. If the battery is failing and you have or want Extended Warranty then you must fit a Porsche Battery - around £220 from an OPC plus fitting. I bought a Bosch silver series one from Costco for £24, currently about £60.

If the battery and alternator check out as David suggests, it could be a dodgy ignition switch - they can cause all sorts of electrical gremlins.

Cheers for the pointers all. Done a few checks and no water under the passenger carpets (car hardly been in the rain, yes I manage to avoid it generally!). Voltage is generally around 13.0-13.5 volts when running which I thought 13.5v was normal, but checking on bits and seeing the posts above it obviously should be close to or on 14v. The car is a 02 model and looking through the history can't find a receipt for a battery change, hard to believe but seems it could be the original battery in there as certainly looks it. I am pinning this down to the battery and on my way to Costco to pick the Bosch Silver one up. Hoping it is nothing more really. Thankfully not got the OPC warranty although keep meaning to get an aftermarket one from a dealer I have used in the past – sods law will need it when I don’t have it. In doing a few checks prior to posting about possible solutions to the problems I see a lot of owners who are weekend drivers use trickle chargers to keep the battery going longer. Problem I have is I park in an underground car park, so no mains source and can’t even use a solar powered charger (used in a previous car when parked above ground and worked well). Guess the main answer is for me to drive the car more often – oh well! Hopefully you won’t hear back from me on this and the battery solves things!

Make sure you have your ignition switched on while you disconnect the battery otherwise the alarm will go off.....its loud ! Also you need the codes for the PCM if you have one, don't know if codes needed for the radio on its own.

Hi I had problem with the battery on my 2004 996 c4s. It was charging and showed 13 volts but didn't last long. I took it off the car charged it and took it to my local garage, They did a load test using special tester and found it had a bad cell in the batery. Could you have the same fault ?

Hi cb Its worth having a look at this if you chnage your battery [link=http://www.porscheclubgbforum.com/tm.asp?m=331718]http://www.porscheclubgbforum.com/tm.asp?m=331718[/link] I had a similar problem. Good volts at the terminal but then the voltage almost disappeard when trying to start the car Steve

Well my trip to Costco was unsuccessful, they had the Bosch Silver for £47 ex but was only the 75Ah version. Apparently they don't stock the 85Ah one going by their internal Bosch catalogue. I have since been informed the equivalent Varta Silver battery is of similar quality using the same technology inside, so may open the search for this as well. Being in London, nearest I can find to the Bosch Silver 85Ah is a Bosch Silver 80Ah battery from Design 911 which is £115. Search goes on…

have a look at Tayna batteries on line, Ive just bought a VARTA (bosch equiv) one for my 996 (80ah model) on line and delivered for £99, and delivered next day.

Thanks for the pointer Warren - Tayna don't seem to have the Silver version with the higher power. I think I have found final success from National Tyres of all places. They do the Varta Silver Dynamic 85Ah for £89, but if you reserve it online you get 10% off the price - £80.10 with a 5 year guarantee. No delivery from them so you have to have a fairly local branch to pick it up. I have to cross the river to the south side of London to get it, but that journey of a few miles can take 1 hour at times! Just waiting for National to call back to confirm it is the correct size, then I can look forward to start motoring again!