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I recently picked up a 991.1 S with very low miles. When I drove her home the battery charge was 14.5v and looked fine. I was playing around with setting the homelink and other items on the PCM. The next day the overnight battery reading showed 11.2v with the car off and I get a low battery / start engine message. I plan to take it to a local shop and do a battery test to determine if I need a new one, but was just curious if other people had similar experience and what ranges was the battery voltage at? Does it appear I need to get a new battery? Any advice is appreciated, thanks in advance!
Last edited by Vinh Nguyen; 05-05-2021 at 11:01 AM.
What year is the car and do you know how old the battery is?
It is almost mandatory to buy a battery tender for your car. Having the car on ACC will drain battery quickly, as DRL is on and car computer drains battery quickly.
So regarding similar experiences, the answer is yes.
If it is the original battery, then it is due for a replacement. You don't need a Porsche branded battery but may need to register it with the car's computer. It is highly debated about the need to do that and I would suggest searching this forum for discussion about it.
With regard to the tender, you don't need a Porsche branded one, which is actually made by Ctek. Forgot the model number but it is not like the newer ones.
that overnight voltage is too low. mine is 12.4-12.3 before starting the engine after being off for days.
The charging voltage looks spot-on, and maybe you just need to drive the car for a while and then look the next morning at the overnight voltage. There are a couple of threads about proper voltage and if necessary changing the battery as a DYO and I recommend you find and read those. I have a 2013 C2S and changed the battery myself. It’s a 30 minute job if you’ve done it before, and an hour tops if you haven’t. Don’t overspend if you get a new battery. You can get an OEM from your dealer discounted - look online at various Porsche dealers’ parts. Also, how old is your battery? It should have a date code on it. If it’s 4 or 5 years old (mine was 6), it doesn’t owe you anything so just replace it to avoid problems in the future. Cost to buy a new OEM battery discounted from a dealer should be about $225 (plus or minus). Cheap insurance.
The charging voltage looks spot-on, and maybe you just need to drive the car for a while and then look the next morning at the overnight voltage. There are a couple of threads about proper voltage and if necessary changing the battery as a DYO and I recommend you find and read those. I have a 2013 C2S and changed the battery myself. It’s a 30 minute job if you’ve done it before, and an hour tops if you haven’t. Don’t overspend if you get a new battery. You can get an OEM from your dealer discounted - look online at various Porsche dealers’ parts. Also, how old is your battery? It should have a date code on it. If it’s 4 or 5 years old (mine was 6), it doesn’t owe you anything so just replace it to avoid problems in the future. Cost to buy a new OEM battery discounted from a dealer should be about $225 (plus or minus). Cheap insurance.
When driving, your electrical system will charge the battery at the maximum rate when in Sport or Sport+ mode. In normal mode, the charging rate is reduced to save fuel, except when the engine is cold and during braking - it's recuperative. Ambient air temperature also affects the charging rate. The colder, the higher.
If you still have the original battery or a Porsche replacement, the date of its manufacture is stamped on the top of the negative terminal (week/year, e.g., 42 over 15). An 8 or 9 year old battery is pretty old.
Found a little round sticker on the side that said 11/17
I guess its not too old, but nearing 4 years
Originally Posted by Southbranch
When driving, your electrical system will charge the battery at the maximum rate when in Sport or Sport+ mode. In normal mode, the charging rate is reduced to save fuel, except when the engine is cold and during braking - it's recuperative. Ambient air temperature also affects the charging rate. The colder, the higher.
If you still have the original battery or a Porsche replacement, the date of its manufacture is stamped on the top of the negative terminal (week/year, e.g., 42 over 15). An 8 or 9 year old battery is pretty old.
05-05-2021 | 10:59 AM
New 991.1 S owner - question about battery charge
