981 battery charging

[GlynMo]

Hi,
I'm new to Porsche ownership and have not had a lot of opportunities to drive mine since I bought it 3 months ago. I therefore decided to install permanent fly leads for an Optimate. After looking at various threads on here and elsewhere, I attached +ive to the +ive battery terminal and -ive to the convenient empty bolt hole on the top left suspension turret. Trouble is, the Optimate indicates that the battery cannot hold a charge, which isn't right as the car starts fine and, if I disconnect the battery from the car and connect the Optimate direct to the battery, it charges as it should. Can anyone shed any light on the problem please?

[Twinfan]

Sounds like the Optimate doesn't like not having a connection to the negative terminal, however this is what the car electronics needs.

If it's charging and working OK, I'd ignore the Optimate message.

[GlynMo]

Twinfan said:

Sounds like the Optimate doesn't like not having a connection to the negative terminal, however this is what the car electronics needs.

If it's charging and working OK, I'd ignore the Optimate message.

There's the trouble, I'm pretty sure it's not charging when connected the correct way.

[Twinfan]

Ah, OK. Above my pay grade then I'm afraid!

Might be time to invest in a CTEK instead?

[elisered]

If you can improve the connection in the bolt hole - clean it out, remove some paint, screw the bolt in tight etc. Or buy a longer lead and connect to the windscreen wiper post. Have you tried your charger on another car? Could be that’s your problem of course.

[GlynMo]

elisered said:

If you can improve the connection in the bolt hole - clean it out, remove some paint, screw the bolt in tight etc. Or buy a longer lead and connect to the windscreen wiper post. Have you tried your charger on another car? Could be that’s your problem of course.

I've attached the Optimate directly to the battery and it behaves as it should. I'll try using alternative earth connections.

[996Targa]

Is there a vertical post over to the left of the battery, to the right of the suspension turret? This is for the negative terminal. I have a CTEK for my car and leave a crocodile clip for the negative on this post and another on the positive battery terminal with the lead trailing alongside the trunk. I leave them on the car all the time.

[anonymous-user]

I can’t find the exact pic, but if you look at the suspension turret below the bolt there also is an empty threaded hole which will fit an M8 bolt. I permanently wired it to my CTEK adapter as the negative.

Eta found the link:

https://www.pistonheads.com/gassing/topic.asp?h=0&...

Works fine with the CTEK but you do need a clean connection. Never tried an optimate.

Edited by anonymous-user on Tuesday 18th May 15:54

[GlynMo]

OK, so I re-attached the neg lead to the bolt hole on the suspension turret after scraping some paint off and now I'm getting meaningful feedback from the Optimate. Trouble is, it's not going into 'maintenance' mode so maybe there is a problem with the battery, although it's showing 12+v even when connected to the car. I think I'll invest in a professional battery test just to see what the truth is. Thanks for your comments all.

[anonymous-user]

My cars are used reasonably regularly so I never use chargers, I just buy new batteries when the old ones are getting tired.

Did the 981S today - now coming up towards 9 years old on its original battery. After receiving an absurd quote from OPC and a pretty silly quote from an indy I checked the procedures on Youtube and sourced a genuine Banner identical replacement from Design911 at £167 delivered. Didn't have to re-set anything at all after the change and just following instructions to switch ignition on and off a couple of times before starting the car.

Strange but true: The secret of success seems to be minimising the amount of "disconnection time" between removing the old battery and connecting the new one. Since all the clamps etc can be removed before you disconnect the battery I reckon my car was disconnected for no more than 30 seconds. And if I've understood correctly so long as you fit a battery of identical specification to the original there's no need to faff about getting the electronics of the charging system reprogrammed.

I've changed batteries in both my cars this month - total cost £250. Dealer quotes had been around £700 for the pair. £450 in my pocket for half a days work and a bit of internet clicking seems remarkably good value!

[Drekly]

Can anyone advise how long a 987 can sit for before it won't start? Is up to 3 weeks OK? Have a charger but would like to avoid needless faffing over spring and summer at least. Car has a new battery.

[Fnumber1user]

Drekly said:

Can anyone advise how long a 987 can sit for before it won't start? Is up to 3 weeks OK? Have a charger but would like to avoid needless faffing over spring and summer at least. Car has a new battery.

Would be a complete guess from anyone without knowing the current state of charge, when it was last used, how cold the ambient temperature has been and is currently etc etc. Just use the thing, or if not possible fit a charger - its hardly a faff, or if it is fit quick connect/plug & play option.

[Drekly]

From fully charged, with an ambient temperature of 16.58 degrees C and with 80% humidity.

[anonymous-user]

Drekly said:

From fully charged, with an ambient temperature of 16.58 degrees C and with 80% humidity.

I reckon a good battery in any modern car should last very easily for a month. Probably three months.

All batteries have a certain rate of slow self-discharge due to the internal chemistry. For car battery in the conditions you describe it might be around 20% a month, making one month lay-up easy and three or more months attainable. The question then becomes how much ongoing current drain there may be due to central locking, alarm system etc. Which brings us back to my guesstimate that one month should be easy and three months may well be achievable.

I try to make sure my cars go out at least once a week and the batteries seems to last for ages. The two I've just changed on a precautionary basis were 8+ (AGM battery) and 6+ years (wet battery) respectively.

[Drekly]

Thanks, good to know. Other half's Mk1 TT barely lasts a fortnight but must have some kind of faulty switch or fuse causing the drain so its always wired up.

[MG Ant]

Cars around 2000 have much higher current drain on immobilizer and other anti-tamper/ anti-intrusion devices... after 2010 or so these systems seem to be much better...