Welcome to 911UK
The only place for Porsche, 911uk is the definitive enthusiast and resource site for the Porsche 911.
Registration is fast, simple and absolutely free, so join up today for full access to the site and benefit from latest member offers.

Porsche Classifieds
Porsche Buyers Guides
Sell Your Porsche on 911uk
Create a Free Classified Advert
Search Ads
Classified Adverts FAQ
Trade Classified Information
Buyer & Seller Fraud Protection
Consumer Rights Act
Pre Purchase Inspection (PPI)
Porsche Car Sourcing
Porsche Cars Wanted
Official Porsche Centre Reviews
Porsche 911
991 : 2011- 14
997 : 2004- 77
996 : 1997-2005 39
993 : 1993-1998 5
964 : 1989-1993 4
Carrera 3.2 : 1983-1989 1
Carrera SC : 1977-1983 2
930 Turbo : 1975-1989 0
Early 911 : 1964-1977 3
Porsche Other Models
Classic : 1950-1965 0
Boxster : 1997- 19
Cayman : 2005- 12
Cayenne : 2003- 5
Macan : 2014- 2
Panamera : 2009- 0
912-914-924-928-944-968 1
959 - CarreraGT - RaceCar 0
Car Parts For Sale & Wanted
Other Items For Sale & Wanted
Wheels Tyres For Sale & Wanted
Number Plates For Sale Wanted

Porsche Services
Porsche Body Shop Repair
Paint Protection & Wrapping
Porsche Classic Insurance
Porsche Classic Parts
Porsche Classic Restoration
Porsche Design Collection
Porsche Engine Gearbox Rebuild
Porsche Heritage & History
Porsche News
Porsche Picture Gallery
Win a New Porsche 911

Porsche Parts
Body Parts, Body Styling
Brakes, Clearance
Electrical, Exhausts
Engine Cooling, Engine Electrical
Engine Rebuild, Heating Cooling
Interior Incar, Lighting
Rubber Seals, Service Parts
Steering, Suspension
Transmission, Workshop Tools
Early 911, 911 - 930, 928 - 968
964 - 993, 996 - 997, Boxster
Cayman, Cayenne, Panamera

Porsche Model Range
911 [991] 2011-Current
Porsche 911 [991]
911 [997] 2004-Current
Porsche 911 [997]
911 [GT] GT1-GT2-GT3
Porsche 911 [GT]
911 [996] 1997-2005
Porsche 911 [996]
911 [993] 1993-1998
Porsche 911 [993]
911 [RS] RS-RSR
Porsche 911 [RS]
911 [964] 1989-1993
Porsche 911 [964]
911 3.2 1983-1989
Porsche 911 3.2 Carrera
911 SC 1977-1983
Porsche 911 SC
911 [Early] 1964-1977
Porsche 911 [Early]
Boxster & Cayman
Porsche Boxster & Cayman
Cayenne & Panamera
Porsche Cayenne & Panamera

911uk Site Partners

Post new topic   Reply to topic
Author Message

Joined: 16 Jan 2015
Posts: 91

PostPosted: Thu Sep 13, 2018 8:31 am    Post subject: Battery voltage and potential replacement Reply with quote


If I know I'm not going to drive my 3.4 for a week or so then I plug it into a CTEK MXS 5.0.

Recently when I do this, the CTEK will intermediately stop at stage 5. The description in the manual is 'tests if the battery can hold charge, checks if voltage drops to 12v, batteries that cannot hold charge may need to be replaced'.

It doesn't do it every time but often enough to conclude that the battery isn't holding charge.

The question is, how low can the voltage go and the battery still operate fine? I drove it on Monday and it seemed to start fine. Just wondering if I need to replace right away or just do it as soon as it becomes slow to turn over.

At the same time, I want to avoid the hassle that seems to go with a completely flat battery so would rather replace ahead of that.

View user's profile Send private message

Joined: 08 Apr 2018
Posts: 159
Location: Cheshire

PostPosted: Thu Sep 13, 2018 2:24 pm    Post subject: Reply with quote

Have you tested/had the battery tested properly rather than rely on the charger?

I would do that before buying a replacement.
View user's profile Send private message

Joined: 16 Jan 2015
Posts: 91

PostPosted: Fri Sep 14, 2018 6:55 pm    Post subject: Reply with quote

Thanks, just put a volt meter on it. It's showing about 12.5 normally, just over 14 when running (so I guess the alternator is fine) and it drops to about 10.5 when I start the engine.

I'm not sure how low it should go when I start, I know lower single figures is bad but is over 10 fine?

View user's profile Send private message

Joined: 21 Mar 2015
Posts: 5975
Location: Brighton

PostPosted: Fri Sep 14, 2018 7:15 pm    Post subject: Reply with quote

10.5 volts on cranking is what a good battery should read .

14 volts running is fine but you really need to have a voltmeter on the battery .. turn lights and any heavy electrical loads on then see what it is at idle .. anything less then 13 volts and your into a worn alternator.

12.5 volts is again a sign of a good battery .

The only other check would be a dedicated battery tester or an acid check which cant be done if the battery is sealed .

If the battery starts the car after 4-5 days without being used in the mean time or connected to a charger then its fine.

My Daughter's Crowdfunding page Here


7pm - 9pm

Now At An Indy.
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic   All times are GMT - 12 Hours
Page 1 of 1

Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You can attach files in this forum
You can download files in this forum
You cannot post calendar events in this forum