IXLR8

Why not? 8 full years out of my factory installed Banner AGM battery and it will soon be going into its 9th year.

For the price of a lithium, I can buy 4 to 5 quality AGMs. The math is really simple.

Porsche_nuts

I am going on year 8 on my original battery.
Since year 5, I have been saying I probably need to get a new battery. Each of those years I have not had any issues, so I just keep on keeping on.

vincenz0

For those of you with 8+ year batteries thinking it's only a matter of time -- A few things will start to get wonky as an indicator that your battery is on it's last legs, here are a few "symptoms" I found on my 991:

• Driver's seat "comfort" entry stops working (where the seat automatically moves back when you open the door to make it easier to get out and then fwd when you close the door)
• Occasionally, the windows won't return to their sealed position after opening the door (they go down a tiny bit when you pull the handle)
• If you try to use the auto start/stop feature, the engine will no longer shut off at a stoplight
• You can't adjust the power seats unless the car is running

I'm sure that's not an exhaustive list, but if you are having any of those issues it could be an indication that your battery is about to go.

WP0

Just changed out the original battery on my 2015 991.1 although it still worked fine, I thought that I was beginning to see a gremlin, and the voltage upon start up showed around 11.0 V, which in an open circuit would indicate less than 10% of battery life left. The manual states that open circuit voltage should be 12.5-12.7 V. The original post here was quite helpful. The only thing I would add is the torque values:
4.5 ft lb for the batttery terminals
17 ft lb for the retaining bar
I assume it’s about 2 ft lb for the T20 torx screws holding the air pump.

edit: For reference, I used the Duracell Ultra Platinum AGM 850 CCA BCI Group 49, and it was perfect fit replacement for the original.

Porsche_nuts

Guessing my luck is running out. Time to start looking for battery replacement.

barncobob

cheap insurance:}

oc911

Battery voltage in the small PCM screen should show ~mid to high 14s after battery replacement. If start crank is weak or voltage below 12 when driving, that’s should be good sign for replacement. Also, battery tender won’t improve a weak battery, believe me I tried

Porsche_nuts

Replaced battery with H8 Die Hard. It makes it manageable to have one foot in the frunk when putting in that behemoth. I don't think I could have done it any other way. A real back saver.

Another tip, lift battery using a cloth threaded underneath the battery handles - makes it easier on the hands, easier to lift, and easier to maneuver.

96redLT4

Bump for a great thread. I guess this counted for semi DIY....Needed to replace the original Banner batter in the car. Lasted 9 yrs! Looked over this thread. Tender, Torx20. Check 10/13 mm sockets. Check. Already to do it with my son. Found a Duracell ultra platinum like in the original post at Batteries Plus. About $250 after taxes and discount/core. Then I saw they offered free same day installation. So....why get my hands dirty and back sore? Went out and ended up helping the tech install it. The one I bought like the OP (SLI49AGM) was H8 and felt really heavy, looked huge compared to the Banner plus it had a manufacture date of 10/23. He let me swap for the same battery but H6 (SLI48AGM). So same dimensions as the original battery, felt lighter and had a little less CCA, I think 760 vs 850. Also it had a manufacture sticker date of 2/24. Only major hitch was when he was taking off the bracket over the battery I said be careful with the hidden bolt into the firewall. Don't let it fall behind the battery. 'Oh sh*t'. Clink clink.There it went behind and underneath the battery tray. Not sure he knew what to do at that point but thanks to this thread and a video I said we need to lift up the battery tray. Now it did become a 2 person job as the tray is attached by multiple wire harness' underneath. I held up the tray and he was able to see the nut but we could not reach it. He said he had a snake like tool with a magnet on the end (which I would not have had at home) and we were able to fish it out. Ended up giving the guy $20 for a beer because he was all alone and looked like he was having a hard day. Took forever to trickle charge the new one at home after a 30 minute drive. Not sure why they are selling batteries 6-12 months old. I thought everything was in short supply after Covid. Thanks RL