Sidvicious7

Alagar

Thanks for the DIY writeup. I took delivery of my car March 2013, so the battery made it 89K miles and almost to 6 years. Auto start/stop hasn't worked for a long time and it's been turning over slower and slower. I got the Batteries+ Duracell with the 20% discount. Replaced it in the parking lot there. Battery was disconnected for about 45 seconds in total with no battery tender connected and I had no loss of settings or errors.

drive95

Thanks for this. I'm setting up to replace my battery in my '14 991. Did your auto start/stop system automatically begin working after battery replacement? Mine hasn't worked in 6 months or more.

Alagar

The auto start/stop did not immediately start working with the new battery, but I presume it is in a discharged state yet. I'll report back in a week or so after I've put some mileage on and the battery has had time to charge.

drive95

​​​​​​​I'll be anxious to hear back. My SA reports that the battery monitoring system the "calibration" resets also controls the start/stop system.

Alagar

I'm happy to report that after 26 miles of highway speed driving into my morning commute, I ran into stopped traffic and the auto stop/start engaged. So, yes, after allowing the battery to charge up the auto stop/start is once again working. I then promptly disabled it

Sajan

I think it's time to replace mine. From what I can tell it's the original battery. Car was manufactured 10/2013.
Battery code on the terminal says "41" on top line and "13" bottom line. I am assuming that means 41st week in 2013 also. (so October).

It's not holding a charge as well anymore since I don't drive it daily. 1-2 times a week and it's not on a tender. Tender is being used by my baby (the 3.2).

The other day it barely cranked over (a whole bunch of errors showed up as it was starting up, like start/stop disabled). It was 40 deg outside. I connected it to the tender and charged it fully. I just went and had auto parts store check it and they said it's a good battery but cranking amps was at 560 now and I need to charge it.

Is Duracell AMG the recommended battery?

eagle1960

IMHO makes no difference. I always buy batteries based on the current price/warranty. Right now Sam Walton is cranking my 991 and 987.

Sajan

I successfully changed the battery.
I went to the interstate store in Houston and picked up a H8 AGM for 184 + tax.

The guy there tested my current battery and when he put load on it, voltage dropped to 8-8.5. He said it should have stayed above 9.6.

I didn't use a battery tender or anything during the swap and as far as I can tell, everything is working.

Unfortunately, the iCarsoft V2.0 is not cooperating when it comes to coding the new battery in. It says communication error; application failure. I emailed tech support, and I will update here. Otherwise I am going to see if my indy mechanic has the PIWIS tool to do it.

zoiks

Need4S

As for not suffering ill effects from swapping the battery while not keeping some power in the system, your OBD readiness monitors will be reset by this and need to start over. Could be no problem if no smog check is imminent, as your normal driving (might) reset them. But if you're going to need a check anytime soon, use something that plugs into your OBD port to keep some current in it while you do the swap.

Joec500

I swapped my battery two months ago and maybe 1500 miles and didn't bother resetting anything on the computer and my car is running just fine. I am not sure if it's really needed, but could be good for peace of mind. I used the same interstate battery as above. My car is a 2013 with 65k miles in Northern California always garaged so no harsh weather and my battery started to get long cranks. My guess is that a car with regular use as you can see from my miles. The batteries are good for about 5-6 years. My local indie said my battery was ok on their tester, but there were times when my starter was struggling, so don't always trust those battery testers

Now with the new battery it's cranks perfect every time.

Sajan

What's the manufacture date on your 991? It's listed on the label on the drivers side door frame.
For the battery date, look on the top of the negative terminal. It should have 4 numbers on there.

Ya I don't trust the battery testers as much. I could tell that it's been slowly taking longer and longer to crank since I pay close attention to it. Mostly because I love the satisfying sound of the start up exhaust.
You need a tester that puts load on it to see the voltage drop. Auto zone said my battery was fine, just low on charge but he did note my cranking amps were only 560. normal for the oem battery is 760? or something like that.

zoiks

From what I can tell the date of manufacture is 12/11 and the numbers on the battery terminal are a 48 over an 11. I assume that is week 48 of 2011. If I'm reading that correctly that is the original battery and I'm probably operating on borrowed time. I just replaced the factory battery in one of my other cars after less than 4 years old. Am I reading all of that correctly?

Sajan

Well that sounds right. For the battery, week 48 = November 28, 2011 - December 4, 2011That matches up with the car being manufactured in dec 2011 also.

You are using an 8 year old battery so maybe it's time. You can always get it load tested and see. Make sure battery is at least 75% charged before you do that.