Stephen Tinker Posted 6November, 2020 Report Share Posted 6November, 2020 For those of you who have a 981 GT4, can anyone give me your running battery charge voltage indicated on the Multi Function Display screen. I've just fitted a new battery (the old one was the original fitted in Sept 2015) but I'm still getting a charging voltage of 14.3 volts (with engine running) which seems a little high to me. This voltage does not drop even after an hours run time. The new battery is fully charged (on the C-tec for 24 hours) and static voltage indicates 12.8v - so fully charged. Any help much appreciated. Quote Link to comment Share on other sites More sharing options...
firstone Posted 6November, 2020 Report Share Posted 6November, 2020 Sounds correct for any alternator to me. Battery level is normal as well. Quote Link to comment Share on other sites More sharing options...
Skidmarks Posted 6November, 2020 Report Share Posted 6November, 2020 2 hours ago, firstone said: Sounds correct for any alternator to me. Battery level is normal as well. What he said. Quote Link to comment Share on other sites More sharing options...
Redracn Posted 6November, 2020 Report Share Posted 6November, 2020 Modern cars especially ones with stop start using AGM batteries have an integrated battery management system that accounts for battery age and usage and adjust S the charging profile and voltages accordingly. 981 is probably in this category as my 991 certainly is. When changing batteries the ECU needs to be told it has a new battery and it’s type and capacity. I have noticed that having the battery on a Ctek seems to upset the integrated charge tracking but more investigation is required. So if AGM battery make sure the ECU is reset accordingly but if car had a more conventional battery then all numbers look ok. Quote Link to comment Share on other sites More sharing options...
Stephen Tinker Posted 6November, 2020 Author Report Share Posted 6November, 2020 Thanks guys - yes I understand re the "new battery" syndrome that the ECU governs the charge rate via the alternator, but I have replaced the original Exide wet cell battery with another of the same make / type and not a AGM. My GT4 does not have a stop / start facility. What's confusing me is that I am not getting any reduction in voltage while driving and the battery is fully charged - the charge rate stays constant @ 14.3v continual and does not drop. The original battery was over 5 years old and I thought that as the ECU was seeing and old battery with some sulfating and was adjusting the voltage "up" accordingly. These new charging systems used to be so simple..... Redracn - an interesting take on the Ctek possibly upsetting the charge tracking. What does your 991 charge voltage look like after startup and running? Quote Link to comment Share on other sites More sharing options...
Redracn Posted 6November, 2020 Report Share Posted 6November, 2020 3 hours ago, Stephen Tinker said: Thanks guys - yes I understand re the "new battery" syndrome that the ECU governs the charge rate via the alternator, but I have replaced the original Exide wet cell battery with another of the same make / type and not a AGM. My GT4 does not have a stop / start facility. What's confusing me is that I am not getting any reduction in voltage while driving and the battery is fully charged - the charge rate stays constant @ 14.3v continual and does not drop. The original battery was over 5 years old and I thought that as the ECU was seeing and old battery with some sulfating and was adjusting the voltage "up" accordingly. These new charging systems used to be so simple..... Redracn - an interesting take on the Ctek possibly upsetting the charge tracking. What does your 991 charge voltage look like after startup and running? In the 991.2 GT3 which has an AGM battery but no start stop etc. the voltage varies quite a bit from over 15V down to low 13s on a long drive. Even after removing the CTEK with a fully charged battery it seems to take a long time for the voltage to reduce but I can not be sure this is not deliberate and part of the batteries conditioning. A constant 14.3V is about right for a wet cell non smart charging system. Have you seen the voltage drop back in the past. If you have a current sensor on the battery negative terminal wiring then you probably have a smart charging system. As the battery ages it’s charging profile changes and swapping to a new battery will see the used battery profile applied to the new battery. Best to find out if your particular car requires the ECU to be reset for a new battery. Quote Link to comment Share on other sites More sharing options...
firstone Posted 7November, 2020 Report Share Posted 7November, 2020 My logic says if there were a " replace battery ecu reset " required it would be noted in it's owner's manual. Might be worth a look? No fluctuations on your dial seems unusual compared to old school or what we've come to expect. Quote Link to comment Share on other sites More sharing options...
Skidmarks Posted 7November, 2020 Report Share Posted 7November, 2020 I recently had to change the battery on my GT2RS. 8 months sitting not good for it apparently. Yes, I forgot to put the trickle charger on ... Simple swap in and out. No ECU reset required. Quote Link to comment Share on other sites More sharing options...
Grimmy Posted 7November, 2020 Report Share Posted 7November, 2020 21 hours ago, Skidmarks said: I recently had to change the battery on my GT2RS. 8 months sitting not good for it apparently. Yes, I forgot to put the trickle charger on ... Simple swap in and out. No ECU reset required. Does the GT-2RS use a light weight lithium based starter battery or just a good old fashioned lead acid one? Quote Link to comment Share on other sites More sharing options...
Skidmarks Posted 7November, 2020 Report Share Posted 7November, 2020 1 minute ago, Grimmy said: Does the GT-2RS use a light weight lithium based starter battery or just a good old fashioned lead acid one? Mine has the Big Boy old style lead acid. But you could get the lithium one as an option. Was one box I didn’t tick! Grimmy 1 Quote Link to comment Share on other sites More sharing options...
Stephen Tinker Posted 8November, 2020 Author Report Share Posted 8November, 2020 On 07/11/2020 at 10:09, firstone said: No fluctuations on your dial seems unusual compared to old school or what we've come to expect. On 07/11/2020 at 09:20, Redracn said: In the 991.2 GT3 which has an AGM battery but no start stop etc. the voltage varies quite a bit from over 15V down to low 13s on a long drive. Even after removing the CTEK with a fully charged battery it seems to take a long time for the voltage to reduce but I can not be sure this is not deliberate and part of the batteries conditioning. A constant 14.3V is about right for a wet cell non smart charging system. Have you seen the voltage drop back in the past. If you have a current sensor on the battery negative terminal wiring then you probably have a smart charging system. As the battery ages it’s charging profile changes and swapping to a new battery will see the used battery profile applied to the new battery. Best to find out if your particular car requires the ECU to be reset for a new battery. Yes you are both correct - these new style alternator controlled ECU's are really complex compared to the older & simpler charging systems. By all accounts, these new systems are to reduce alternator "drag" on the engine while charging (especially in heavy stop / start traffic) which reduces load and increases fuel economy. I drove for about an hour yesterday and the indicated voltage went down from 14.4v to 14.2v on the meter. I also had a plug in voltmeter (plugs into the cigarette lighter) and my old Fluke meter and they all registered the same state of voltage. Another interesting puzzle is the GT4 has a SPORT button which gives you a throttle blip on gear down change and lowers the coolant & oil temps by electrically opening the thermostat fully. This SPORT button also increase the alternator charging voltage by +/- 1 volt for some reason nobody can explain but it shows on the voltmeter - except mine doesn't.... Go figure! Next step is to plug my Durametric in and see if I can change the charge rate or battery profile. Quote Link to comment Share on other sites More sharing options...
Redracn Posted 8November, 2020 Report Share Posted 8November, 2020 A lot of cars now have a small amount of regenerative braking using the standard alternator and battery which along with start stop is really hard on the battery. The problem is that regenerative braking can only happen if the battery is not fully charged. So the ECU keeps the battery at a lower charge state by using it to help run the car electrics. As well as a tiny fuel saver this is also a performance advantage basically similar principle to F1 KERS. So it would be reasonable for the battery charging to be adjusted for max performance in sport mode which would mean pushing in as much charge as possible during braking so the alternator makes no drag on the engine when at full throttle as the car can now run all/partially on the battery. This is 25year old race stuff. Good idea to log stuff independent of the car systems as a lot of data especially what is present to the driver is highly doctored. Quote Link to comment Share on other sites More sharing options...
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