CSK 911 C4S

Thanks daberlin for this info.

I just installed the Batteries Plus Duracell as well.

Pretty straight forward and I changed it out w/o using any auxiliary power source and nothing had to be reset.

cookie monster

Just another note of thanks to Daberlin and the other contributors, great write up and pics. I've got a 2014 so will be looking to change the battery soon, planning on doing so without using an auxiliary power source.

slingshot60

daberlin

Good job.

As there is no battery vent tubing in the 991, just leave the vent elbow on the battery alone and not plug it up.

StormRune

The 991 models are designed to use completely sealed AGM batteries with no vents. Conventional batteries however emit a significant amount of hydrogen when charging and a bit of sulphuric acid gets carried along with that. That is why prior 911s with conventional batteries ran a vent line out into a well ventilated area (under the car)... probably as much for getting the acid out of the car as much as the hydrogen.

On cars with conventional batteries and no lines attached to a vent (or ones that just breath through the caps) you tend to see a lot of acid build-up and corrosion of parts around the areas where the battery breathes... the terminals being one nearby spot that commonly gets this build-up and the mounts around the battery another. Substantial corrosion is what you will certainly see happen over time if you don't run a proper vent... not to mention the potentially explosive effects of hydrogen if it finds a spark. It's rare but it occasionally happens (usually when trying to jump the battery or disconnect the terminals).

Ideally you should use an AGM battery and if not, you should find a way to vent the battery out into the open air. BTW, AGM batteries also tend to have more charge/start cycles so they will typically last longer helping offset their higher cost if you keep the car longer than a handful of years.

SDaddy

Hopefully battery reset functionality is on their roadmap. It is something an "enthusiast" does. "Coding" is apparently in the professional model.

bittrl1000

When you see a conventional wet-cell battery with a vent tube, it's because the battery is on the inside of the firewall. The tube vents the gas outside the passenger compartment. Normal cars, with a wet-cell battery in the engine compartment, don't have vent tubes.

slingshot60

So... did I screw up with the Interstate battery? Should I yank it and put in an AGM?

Sidvicious7

sdl2112

FYI...I'll soon need a battery so I called Interstate and they say the Mega-Tron Plus is NOT an AGM type, just a standard wet cell. AGM requires a higher charging voltage so I would be concerned using a standard type.

bittrl1000

If you have the battery in front of you, it's easy to tell. If you see, hear, or feel liquid sloshing around when you shake it a little bit, it's a wet-cell. If there's a vent hole or tube, it's a wet-cell.

Porsche_nuts

Interstate AGM

https://www.interstatebatteries.com/...ategoryid=true

Sidvicious7

stealthboy

Just ordered the same battery as OP, and will be installing this weekend. I have a 2013, and noticed that it's been taking longer to start, and recently the auto stop/start has stopped functioning completely (just get the yellow A with the line through it). Not that I use auto stop/start, but it's an indicator that the battery is not maintaining a decent enough level to have systems running without the engine on.

Thanks for the writeup! Looks straightforward.

LexVan

This made me chuckle a little. I workout 5 days per week. For my age, I can hold-my-own pretty well in the weight-room, even with guys 1/2 my age. I don't think I can shake a 50-60 pound battery. Thank you.