This week I was surprised to have a flat battery immediately after an hour motorway drive. Yes the battery is 4 years old (original Porsche banner battery), but I would think after an hour motorway drive I would be able to get my wallet out of the luggage compartment after I parked the car. But the battery so flat.
I usually drive in Sport mode, however, on this particular journey I had the Mrs with me and was just having a relaxed drive on Normal driving mode. It was during the day, no headlights, no heated seats.
Porsche assistance found the battery has 11.7V. They did a jump start then on testing the battery on idle the battery was not taking charge but after the technician turned the light on the battery started to be charging. I guess this is something to deal with "smart alternator charging".
After arriving home I connected my MXS- 5 cteck on Recond mode till battery was fully charged.
Today, I had the car for a drive and noticed the vehicle volt on the dashboard as seen in the attached pics. When driving on Sport mode, the car voltage is usually between 14.6 to 14.8V. As soon as I cancel the Sport mode and drive in Normal mode the voltage drops to around 12.4V. This kept happening every-time I switched between sport and normal. It was independent of A) electrical load: ie turning on main head-beam, air condition, and seat heater didn't affect the car voltage. B) Engine Rev: changing the RPM didn't have a noticeable effect on the car voltage.
So, am I getting this right: in normal driving mode the dynamo is hardly charging the battery?!?!? is this normal or I have a problem with the dynamo? Can someone please check if their vehicle volts behaves similar to mine. (991.1 C4S, 2014)
I noticed something strange as well with the charging system also. I leave my car on battery tender since it is not daily driven. When I drive it and it is usually on long trips in normal mode I notice when I hook up the battery tender it takes 8-12 hours for it it be fully charged. I also have a BMW which is also on battery tender and after I drive it it says fully charged within an hour or so.
It could be that Porsche has given fuel efficiency more importance than making sure to keep the battery fully charged ? If alternator is heavily working all the time, for sure it could have an impact on fuel consumption.
My car is new (January 2018), it's a daily driver and I have done some long trips with it. I would have though that the battery was OK when I first plug it to a charger on April..... but I was wrong. My Optimate 6 charger indicated that the battery was low and it took a long time to charge it to full capacity. After that experience and reading about similar experiences, I decided to install a permanent connector for the battery in my car and now I charge the battery at least once a week. I do leave the car connected also when I'm traveling Hopefully that helps to extend the life of it.
Modern Porsches have regenerative braking, much like hybrids. That is to say they have a high capacity smart alternator and programming to charge the battery mainly during braking. This provides more power during acceleration and better fuel economy when cruising. I always use Sport +, but not sure that affects charging. I do use plenty of engine braking via early downshifting. This is an additional reason why I always connect my CTEK maintainer any time my Porsche will sit more than 3 days. The other reason I often use the maintainer is these modern Porsches use battery power while parked, and sulfation "happens". So get a good maintainer and try to use it at least once a week.
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