Battery advice
Thread Starter
Burning Brakes
Joined: Oct 2016
Posts: 758
Likes: 308
From: Zzz
Battery advice
Hi Folks,
I'm thinking my battery is coming to an end...voltage is around 11.7-11.9 when I first turn the ignition on (before the car is started). Voltage is high 14s-15s when driving. I've seen the thread where someone changed his battery without issue but the manual says the car ECU must be updated after the battery change. Is this really necessary? Dealer cost for a battery is quite high.
I'm also concerned because I have an extended warranty and would hate for them to deny coverage on an electrical problem citing the battery as an issue.
Thanks for your help,
NF
I'm thinking my battery is coming to an end...voltage is around 11.7-11.9 when I first turn the ignition on (before the car is started). Voltage is high 14s-15s when driving. I've seen the thread where someone changed his battery without issue but the manual says the car ECU must be updated after the battery change. Is this really necessary? Dealer cost for a battery is quite high.
I'm also concerned because I have an extended warranty and would hate for them to deny coverage on an electrical problem citing the battery as an issue.
Thanks for your help,
NF
Racer
Joined: Sep 2016
Posts: 350
Likes: 15
From: SF north bay
Totally up to your personal comfort level.
If you do it, plug the car in via any decent charger + cigarette lighter feed. In a pinch (before I got my Ctek) I bought a $10 9V battery device that connects via cigarette lighter and supposedly saves the ECU settings... It worked in that I only had to reprogram the windows, nothing else popped... I'd prefer the Ctek Approach though, uninterrupted power. I fail to see any electrical issues caused by you changing your own battery. Especially if power is never cut... If that were an issue, dead batteries would mean your 991s must be thrown away ;-)
If anything your current battery is practically dead and that might do harm and cause glitches (at least make your alternator work overtime). You could always ask the dealer to do the ECU thing at next service - I've had a few cars with this requirement, always ignored it with no consequences. I think worst case the battery is not recharged "optimally" by german standards, but it's been totally fine so far... I look at voltage every day and my alternator works a lot less hard than it used to, but still within normal range (generally 13.5V).
If you do it, plug the car in via any decent charger + cigarette lighter feed. In a pinch (before I got my Ctek) I bought a $10 9V battery device that connects via cigarette lighter and supposedly saves the ECU settings... It worked in that I only had to reprogram the windows, nothing else popped... I'd prefer the Ctek Approach though, uninterrupted power. I fail to see any electrical issues caused by you changing your own battery. Especially if power is never cut... If that were an issue, dead batteries would mean your 991s must be thrown away ;-)
If anything your current battery is practically dead and that might do harm and cause glitches (at least make your alternator work overtime). You could always ask the dealer to do the ECU thing at next service - I've had a few cars with this requirement, always ignored it with no consequences. I think worst case the battery is not recharged "optimally" by german standards, but it's been totally fine so far... I look at voltage every day and my alternator works a lot less hard than it used to, but still within normal range (generally 13.5V).
Intermediate
Joined: Dec 2016
Posts: 39
Likes: 3
Yes, change it before you get stuck. Mine was doing the same plus auto stop/start was disabled. I changed my battery last night and only reset the windows and clock. Everything else was saved. I did not use anything to maintain power. I have a Ctek but not sure how that would work without a battery present. I'd think it would go into the error state. No errors today and the start/stop works again.
Instructor
Joined: Apr 2016
Posts: 126
Likes: 2
From: Austin, TX
Ok so sorry for the rookie question but what should the voltage be while running and before you start it? I've had my car almost a year and it's always been in the 14s while driving. I honestly haven't looked at it before starting but will tomorrow.
Instructor
Joined: Feb 2016
Posts: 242
Likes: 12
A mostly charged sealed-lead acid battery should be somewhere between 12.5V-13V. Keep in mind the the open circuit voltage (OCV) of a battery like this does not tell you whether the battery is good. OCV only tells you the state of charge. To determine whether a car battery is good, you first need to make sure it's charged. Then you place a certain load on the battery, all while watching how the voltage responds.
Once the car is started, the alternator should raise the voltage to around 14V. If the voltage stays the same as it was before you start the car (or if the voltage drops), then your alternator is likely bad.
Once the car is started, the alternator should raise the voltage to around 14V. If the voltage stays the same as it was before you start the car (or if the voltage drops), then your alternator is likely bad.
Racer
Joined: Sep 2016
Posts: 350
Likes: 15
From: SF north bay
On the 991 it's hard to measure exact battery voltage because once you pop the front trunk, you have awoken the beast already. Some modules are active and suck 0.2 to 0.3 V - I know this because after unplugging my old battery it read higher outside the car.
Same if you insert the key and look at the voltage without starting. 12.5V or 12.6 for me.
My stock 2013 car battery dated back to 2012 and my alternator was always outputting 14V+ , close to 15 at times. I changed my battery preemptively and now my alternator sits between doing nothing - 12.6 - to working a lot less -13.5 to 13.8. Only in sports mode do I see 14.x anymore. Feel free to draw your own conclusions but I prefer it that way. :-)
Same if you insert the key and look at the voltage without starting. 12.5V or 12.6 for me.
My stock 2013 car battery dated back to 2012 and my alternator was always outputting 14V+ , close to 15 at times. I changed my battery preemptively and now my alternator sits between doing nothing - 12.6 - to working a lot less -13.5 to 13.8. Only in sports mode do I see 14.x anymore. Feel free to draw your own conclusions but I prefer it that way. :-)
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Thread Starter
Burning Brakes
Joined: Oct 2016
Posts: 758
Likes: 308
From: Zzz
So your brand new battery was only 11.9 before the engine was started? Interesting...mine is around 11.8-11.9 before I start the engine. Once running though I'm usually in the high 14s or low 15s.
Cheers,
NF
Cheers,
NF
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Instructor
Joined: Apr 2016
Posts: 126
Likes: 2
From: Austin, TX
So I just started the car and before it was started the volts were at 11.6 and did change (30 sec) before I started it. Once started I stay at 14.9-15.1 does this mean my battery is almost dead? (Assuming I read the OP correctly)
Last edited by Austin-Guy; Jan 28, 2017 at 02:24 PM.
Thread Starter
Burning Brakes
Joined: Oct 2016
Posts: 758
Likes: 308
From: Zzz
Wanted to thank everyone for their sage advice. Did replace the battery today with a Duracell Ultra AGM Type 49 battery (technically an H8 battery but our battery tray has the room). Weighs a few pounds more than the original battery but does come with a 4 year replacement warranty (best I could find locally).
As for the install, Greg's DIY guide is spot-on (thanks for taking the time to make it for us Greg!). I kept a CTEK 3300 plugged in while disconnecting the battery and had no issues. No faults, no need to reset radio presets, time, TPMS, windows, or sunroof. So far car is driving great. Since I used a larger battery with more CCA I am wondering if I should ask the dealer to reprogram the car for the battery...I suspect they'll charge me over $100 to do that and it's probably not worthwhile if the benefit is to prolong the life of a $200 battery. If there's another benefit to reprogramming the car for the battery I hope someone will let me know.
Cheers,
NF
As for the install, Greg's DIY guide is spot-on (thanks for taking the time to make it for us Greg!). I kept a CTEK 3300 plugged in while disconnecting the battery and had no issues. No faults, no need to reset radio presets, time, TPMS, windows, or sunroof. So far car is driving great. Since I used a larger battery with more CCA I am wondering if I should ask the dealer to reprogram the car for the battery...I suspect they'll charge me over $100 to do that and it's probably not worthwhile if the benefit is to prolong the life of a $200 battery. If there's another benefit to reprogramming the car for the battery I hope someone will let me know.
Cheers,
NF
Rennlist Member
Joined: Sep 2014
Posts: 2,207
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From: Northeast
The AGM battery you installed "must be coupled with "registering" the battery replacement with a factory level scan tool, or the battery life will be severely shortened".
Apparently, AGM batteries require a special charging system strategy that changes as the battery ages.
Pro
Joined: Nov 2006
Posts: 555
Likes: 59
From: Chester VA
Per Excellence Magazine - June 2017
The AGM battery you installed "must be coupled with "registering" the battery replacement with a factory level scan tool, or the battery life will be severely shortened".
Apparently, AGM batteries require a special charging system strategy that changes as the battery ages.
The AGM battery you installed "must be coupled with "registering" the battery replacement with a factory level scan tool, or the battery life will be severely shortened".
Apparently, AGM batteries require a special charging system strategy that changes as the battery ages.
Rennlist Member
Joined: Sep 2014
Posts: 2,207
Likes: 445
From: Northeast