Caution on fully charging bmw e70 battery

[Crowz]

Originally Posted by dreamalaska

To clarify, did you disable the the Intelligent Battery Sensor by just bypassing the device mounted on the negative battery terminal? Thx


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Yep thats the one.


I unplugged its lead.

[andrewwynn]

On my recent 850 mile drive I was curious about the alternator charging program so I pulled up voltage display on bimmerlink.

Going through the mountains I noticed the voltage drop to ≈ 12.3 going up hills and 14.8 when going down hills.

I think the IBS aims to keep the battery at about 80% charge so it always has room to take charge while coasting. I do wonder how often it charges when driving over a completely level road.

https://bimmerscan.com/bmw-intellige...ry-sensor-ibs/

[Crowz]

Originally Posted by andrewwynn

On my recent 850 mile drive I was curious about the alternator charging program so I pulled up voltage display on bimmerlink.

Going through the mountains I noticed the voltage drop to ≈ 12.3 going up hills and 14.8 when going down hills.

I think the IBS aims to keep the battery at about 80% charge so it always has room to take charge while coasting. I do wonder how often it charges when driving over a completely level road.

https://bimmerscan.com/bmw-intellige...ry-sensor-ibs/

Not very often. I monitored mine for a month solid before I pulled the plug on it. Deceleration was always a charging event but otherwise it didn't do much. I couldn't believe how often I would see it at 12.3 or so while driving on flat ground. I had seen it get into the high 11's in certain situations. That's unacceptable to me.


If it wasn't for my dashcam cutting off I would of never known it was doing this. It never kept the battery charged to the levels I wanted but I never knew it was just barely running the car most of the time. It may save a mpg or so but I would rather have the battery charged.

[andrewwynn]

I think you can code out the charge when coasting. Unless you drive mostly short drives and plug in when home I doubt you'll be doing the battery any favors disabling the IBS.

I thought about doing that but then I'm a big fan of the mog I get and have no negative impact from the wildly changing voltage.

[Crowz]

If someone wants to check this out before pulling the plug on it I suggest getting one of the volt meters that plug into the cig socket. That's what I did. Its perfect since the car turns off the power to the socket when you turn the car off.


This looks like the one I have (I don't remember the exact model I have) and its a 4 pack for $12 so a pretty good deal if you have multiple vehicles.


https://www.amazon.com/12V-24V-Digit...983762&sr=8-21

[josiahg52]

Originally Posted by andrewwynn

On my recent 850 mile drive I was curious about the alternator charging program so I pulled up voltage display on bimmerlink.

Going through the mountains I noticed the voltage drop to ≈ 12.3 going up hills and 14.8 when going down hills.

I think the IBS aims to keep the battery at about 80% charge so it always has room to take charge while coasting. I do wonder how often it charges when driving over a completely level road.

https://bimmerscan.com/bmw-intellige...ry-sensor-ibs/

Well, that sort of makes sense. Let it float going uphill when the most power (fuel) is required and top it off going downhill when you're coasting. The whole point is to economize after all and "optimize" battery state. It's like regenerative braking.

[josiahg52]

Originally Posted by Crowz

Diesel models probably charge the battery differently I would imagine.

Quite possible.

Seems like a pretty dumb Intelligent Battery Sensor if overcharging is occurring.

[andrewwynn]

It's exactly regenerative braking. Just at a very small level. Small enough I really wonder if it's worth the effort. Once battery is charged the alternator has very little drag only to power live loads. If I can find the setting in bimmercode I may do an experiment to try determine mpg difference.

[Crowz]

One other thing that I found out after pulling the plug was how well everything else worked on the car.


AC fan seems to blow harder (could be an illusion, can't prove this one)


Power windows are VERY much improved. The windows go up and down noticeably faster (This one is fact. No problem noticing it right off the bat)


Lights are brighter at night. Doesn't effect headlights but the interior lights are brighter.


Dashcam actually charges its battery for the first time correctly. I had a real issue on this one. First I figured I wasn't driving enough so I replaced the internal rechargeable battery which doubled its capacity. This made it go longer before reaching the dead point but still wasn't staying charged. After the ibs change it stays charged all the time now.


The wife's 535xi has a Chinese alternator on it (was on there when I bought the car) that the ibs can't deal with so it works likes its unplugged. This actually drove me up the wall on my original testing since my x5 acted stupid charging wise and the car worked great with the two being almost identical motor and electrically.


I'm not saying everyone needs to do what I did but I would suggest at least running the volt meter to see what is really going on for yourself. Then deciding if you want to try it. Its just unplugging a wire and if you don't like how it does then plug it back in

[Crowz]

Originally Posted by josiahg52

Quite possible.

Seems like a pretty dumb Intelligent Battery Sensor if overcharging is occurring.

Maybe not. I think the goal of this was more epa/mpg cheating. Just like the stupid cutting the motor off at a stop. Just a way to cheat the mpg numbers.


With a diesel they don't have the same "need" to cheat I would imagine. Plus if you don't keep a diesels battery fully charged your going to get cranking problems and pissed off customers.


To risky to try the cheat on those.


Again all guessing but I could see this playing out that way.


Volt meter will tell you right quick. It loves to stop charging while driving. If you never see it dip under 13.8 or something then the diesel isn't doing the no charging stuff.