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Mine always used show around 14.2-14.3 but recently started going up and now it is around 14.8-14.9 ( always on sport mode) it is 2014 991 base. Is there a thing to be concerned? Thanks
Normal in the fall/winter, as the temperatures get colder the charging voltage rises. As mentioned above you might even see it hit 15V on occasion.
Good thing know.
Mine is running around 14.5v while driving. However it is indicating 12.0 to 12.1 volts when off.....
Car starts and runs fine. Hasn't gotten cold here yet. But it does see short trips. Problems?
Enjoying this topic, I hope I'm not repeating myself too much and that I'm not full of $#%^... On a normal (older) car, 12.0 to 12.1 would be terrible. I replaced mine because it showed 12.2... On my old porsche that would mean nearly DEAD - and extra work for the alternator. Yet the 991 was running fine and - surprisingly - starting fine, BUT it was charging at 14.8V+ most of the time, which I still think is abnormal... I'm not sure why we claim this is OK, but I did not own my car from new either... measure what your battery charger puts out, it's lower than that.
The odd thing was when I replaced my original 4y old Porsche battery and tested it out of the car (disconnected), it showed 12.5V without me recharging it. So my guess is by the time you have popped open the trunk, you've awoken the some of the car's electronic components and they are sucking on the battery giving you a false reading by 0.3V. So even if you measure Voltage at the battery terminals, engine off, you'd get 12.6V (best case) minus the suck from those modules.. So I was getting 12.2, you get 12.0... Yours is probably deader...probably 12.3-12.4 real life - disconnected, meaning on the way out...
The only correct measurement would be to disconnect your battery from the car when testing, but that's risky (?) and annoying (reprogramming etc)....
See what you get if you turn the ignition to position 1 with the voltage shown on the dash, but without turning on the engine? Probably the same 12V - which would be too low IMO...
I don't know a thing about this car's electronics nor modern AGM batteries, I just know that supposedly, a full battery is 12.6 or even 12.7V... 12.0 is pretty much a boat anchor, if that's the true voltage... I posted a chart earlier... I can tell you that while my car was running fine, the original Porsche battery NEVER finished recharging with a CTEK charger despite being on the juice for 2 full days straight. The replacement battery (always a little low when you buy it) recharged FULLY in 4 hours. (hint #1)
I can also tell you that since I put in the new battery, the voltage shown on the MFD is pretty much constantly 12.6 to 13.5V (hint#2). It spikes to 14.5 once or twice for a few seconds on my 45 min commute, never more... Before (old battery), my car was *constantly* between 13.9 and 14.8V. In my book the car was perpetually charging a dying battery, but it still started well enough.... Odd. Guess#2: This starter is designed to run with the auto-stop-start feature, so *maybe* it's really efficient, high torque, despite lower voltages ?
Also I tried seat heaters on, headlights, etc... whatever, I'm seeing only 13.5V most of the time, happy place for me...
Guesses aside, I figure that a 4y old battery in a modern car such as ours is a wear item. It's $200. I betcha an alternator costs way more, and now mine is no longer working like a hamster on a wheel... IMo those of you that see 15V and whose car is >3y old should at the very least use a battery tester. I just don't see 15V as normal, maybe "common" on older cars, but not normal... Again, please draw your own conclusions, I am no expert, just stating what I saw and think is logical.... Maybe I'm wrong ;-) (but I'd buy a new battery ;-)
Enjoying this topic, I hope I'm not repeating myself too much and that I'm not full of $#%^... On a normal (older) car, 12.0 to 12.1 would be terrible. I replaced mine because it showed 12.2... On my old porsche that would mean nearly DEAD - and extra work for the alternator. Yet the 991 was running fine and - surprisingly - starting fine, BUT it was charging at 14.8V+ most of the time, which I still think is abnormal... I'm not sure why we claim this is OK, but I did not own my car from new either... measure what your battery charger puts out, it's lower than that.
The odd thing was when I replaced my original 4y old Porsche battery and tested it out of the car (disconnected), it showed 12.5V without me recharging it. So my guess is by the time you have popped open the trunk, you've awoken the some of the car's electronic components and they are sucking on the battery giving you a false reading by 0.3V. So even if you measure Voltage at the battery terminals, engine off, you'd get 12.6V (best case) minus the suck from those modules.. So I was getting 12.2, you get 12.0... Yours is probably deader...probably 12.3-12.4 real life - disconnected, meaning on the way out...
The only correct measurement would be to disconnect your battery from the car when testing, but that's risky (?) and annoying (reprogramming etc)....
See what you get if you turn the ignition to position 1 with the voltage shown on the dash, but without turning on the engine? Probably the same 12V - which would be too low IMO...
I don't know a thing about this car's electronics nor modern AGM batteries, I just know that supposedly, a full battery is 12.6 or even 12.7V... 12.0 is pretty much a boat anchor, if that's the true voltage... I posted a chart earlier... I can tell you that while my car was running fine, the original Porsche battery NEVER finished recharging with a CTEK charger despite being on the juice for 2 full days straight. The replacement battery (always a little low when you buy it) recharged FULLY in 4 hours. (hint #1)
I can also tell you that since I put in the new battery, the voltage shown on the MFD is pretty much constantly 12.6 to 13.5V (hint#2). It spikes to 14.5 once or twice for a few seconds on my 45 min commute, never more... Before (old battery), my car was *constantly* between 13.9 and 14.8V. In my book the car was perpetually charging a dying battery, but it still started well enough.... Odd. Guess#2: This starter is designed to run with the auto-stop-start feature, so *maybe* it's really efficient, high torque, despite lower voltages ?
Also I tried seat heaters on, headlights, etc... whatever, I'm seeing only 13.5V most of the time, happy place for me...
Guesses aside, I figure that a 4y old battery in a modern car such as ours is a wear item. It's $200. I betcha an alternator costs way more, and now mine is no longer working like a hamster on a wheel... IMo those of you that see 15V and whose car is >3y old should at the very least use a battery tester. I just don't see 15V as normal, maybe "common" on older cars, but not normal... Again, please draw your own conclusions, I am no expert, just stating what I saw and think is logical.... Maybe I'm wrong ;-) (but I'd buy a new battery ;-)
Well that's after a week +, with my fresh new battery. Headlights on, seat heater on, heater on, PCM on. I managed to catch it transitioning from 13.4 to 13.5 ! oops... (and yeah I prefer celsius ;-)
I still don't think 14.8 is normal, but you go with what makes you comfortable, I'm not offering any proof. My old porsche battery would spend 2 days on the Ctek and never get to green (almost but not quite) and I'd see 14.8 all the time. No more. I see 14.5 for a few seconds every now and then, but by and large it sits around 13.5V since the new battery...
Don't know what Greg went with but I used an H8 Duracell Ultra Platinum AGM from BatteriesPlus and it works great. (I later found out it's even cheaper at Sam's club) If I'm not in sport mode my voltage is 13-13.5. With sport on it's in the low 14's. I never see 15 anymore (and my car with stuck at 15 with the old Porsche battery).
I went to the local NAPA store and got something of the same size - it had a better CCA rating even. I don't recall the brand and it's pouring rain on my car (since december and seeminly till april, in drought stricken cali!)...
I would not overthink it too much, all the store have a size/rating equivalency.
Thanks for posting the pic of the voltmeter GregD. I have a 2015 C2S and guess what........no voltmeter. Looked all over for it. See pic.
So cannot really check battery on my own. (voltmeter at other location) Guy at Sams said he'd check it. Found a Duracell H8 (Group 49) battery there. Existing battery is 27cm wide.....new one will be 35cm. Those bolt holes are spaced exactly 4cm apart, so new battery
$169 at Sams for Duracell AGM Platinum with 3 yr warranty, $229 at Batteries Plus for Duracell AGM Platinum Ultra with 4 yr warranty. Duracell shows only Platinum on their site, so I think the Ultra is some special deal for Batteries Plus only and the extra cost covers the additional warranty. (you can get a 10% discount code so brings it down to $205). I'm going with Sam's as seems like the better deal.will be the largest this battery box can handle. See pic.
I'll figure this car out eventually ! Thanks again for posting the pic GregD........sent me in the right direction in the manual. Shows 11.6 now, but that's with engine off and things running. I'll test 'er out more tomorrow.
Q is - and I searched -.. Do I really need to get the dealer to teach the ECU about my battery or is it BS ? Should I really invest into another power source to maintain power while I do the swap, or just do it, let the car sort if out after a few miles ? Ah - modern cars....
By the way, did anyone ever answer the original question? I guess GregD indicated he is not sure that maintaining the power did much but he only had to reset the windows. But the bigger issue, what about the dealer teaching the ECU? Specifically, my manual says "After you install a new battery, it must be initialized in the control unit. Please contact your authorized Porsche dealer". The guy with the BMW made a case for this when changing the battery size, which I intend to do. Does anyone have any further info on this, or is it possible for an owner to initialize the new battery in the control unit??
11-01-2016, 02:44 AM
