OV9

Interesting discussion. I will be exploring this soon once I have a drive as quite frankly I'm tired of cars bonging at me that they have low battery.

Equally I'm not going to be opening the bonnet of the 911 and removing the plastic coverings to get at the battery each time. Same for the RR which I believe has one under the boot floor and one in the side with jump posts in the engine bay.

Doesn't Harry M use the pigtails without issue and I thought had indicator lights showing SOC?

Alfa had posts under the bonnet - you had to use these for jump starting but the *recommendation* was to use the posts under the engine bay for charging as well.

Quick search shows that BMW also says to only using the posts due to IBS (battery sensor, not because it causes explosive bowel movements).

Matty wrote: Wed Mar 18, 2026 10:27 am Alfa had posts under the bonnet - you had to use these for jump starting but the *recommendation* was to use the posts under the engine bay for charging as well.

Quick search shows that BMW also says to only using the posts due to IBS (battery sensor, not because it causes explosive bowel movements).

That’s the general rule for cars with battery management, hence I’ve always followed it.

(Also the CTEKs with the led indicator which is always on will bong up a increased rate of battery discharge message on BMWs)

GG. wrote: Wed Mar 18, 2026 10:17 am Equally I'm not going to be opening the bonnet of the 911 and removing the plastic coverings to get at the battery each time.

That's why you fit the permanent extension lead - you run the end of it to somewhere convenient.

If an Intelligent Battery Sensor can't cope with a battery being charged, it's not very intelligent is it. However, that's a different question to using the jump start terminals near the engine; a CTEK only outputs a relatively small current and you want that to be as direct to the battery as possible rather than through the resistance of the car's body. I don't have an IBS on any of the cars I've attached permanent quick connectors to, but if you do then there should be a post near the battery to connect the black lead to.

It’s because you’re bypassing the sensor by charging directly. It’s why when you fit a new battery you code it. The car will relearn over say 30 mins without it but until then it could be charging a fully charged battery.

Mito Man wrote: Wed Mar 18, 2026 1:09 pm It’s because you’re bypassing the sensor by charging directly. It’s why when you fit a new battery you code it. The car will relearn over say 30 mins without it but until then it could be charging a fully charged battery.

Charging a fully charged battery - oh noes! Just like any car without an IBS then. It's a sensor, it senses the battery's current state of charge when the alternator isn't running. It can sense the battery's state of charge after it has been charged. There's a lot of guff spouted about an IBS but the fact is that on any 20yr old BMW it's probably not working properly anyway and stopping your car charging when it should.

A failing IBS will throw a code and a totally dead one will result in the car not even turning over as it assumes the battery is dead. So the majority of cars on the road which are running will have a healthy IBS. Even at 20 years old. They typically fail because people jump start them at the battery terminals bypassing the IBS…
And the car in my photo wasn’t even a BMW.