[thealbert]

I have a 2012 F10 535i. I had a P3Cars Vent Integrated Data Display and Boost Gauge (http://www.turnermotorsport.com/p-17...i-m5-2011.aspx) installed on my car, so I've been able to monitor a lot of things that's going on behind the scenes in the car.

I periodically check my battery voltage and when I normally run my car, the voltage was around 14.4v to 14.7v all the time. But now for some reason, now, it's always at around 13.3v to 13.9v. Even when I run/accelerate the car, its only at 13.3v. Before when I would accelerate on my car, the voltage would go up. Sometimes even up to 15v+. But now, under acceleration, the voltage seems to be not affected at all. But when I hit the brakes and the efficient dynamics blue bar fills up on the dashboard, the voltage jumps back up to 14.7v during the time the blue bar is active. I assume this is the system charging the battery?

When I am idle at a stoplight, the voltage drops to about 13.0v. It used to hover higher, at around 14.3v. Also, when coming to a stop, just at the point when the car stops, the voltage would drop to about 12.5v and the car would shudder for a very quick second. I've never noticed this before as well.

I normally drive with my start/stop system off but decided to give it a try today and that's when I noticed the battery voltages not being the same as what I used to see. Also, when I would normally see the 14.7v voltage, I would only drive my car about once a week. Lately, I've been driving my car everyday. Could it be that my battery was getting drained back in the day and hence why my car always registered 14.7v as the car was constantly charging my battery? Now that I drive it everyday, the battery's got more juice and thus the constant 13.3v?

I'm not battery expert and I know most people don't normally monitor their voltage of the battery while driving but I'm wondering if this is normal? Could there be something up with my battery or alternator/charging system? On my other cars, I know anything in the 13v range denotes a healthy battery but I an unfamiliar with the battery specs for the F10. I am most puzzled with the fact that the car's voltage used to be at 14.7v when running and now it's suddenly dropped to about 13.3v.

[FenixMike]

Originally Posted by thealbert

I have a 2012 F10 535i. I had a P3Cars Vent Integrated Data Display and Boost Gauge (http://www.turnermotorsport.com/p-17...i-m5-2011.aspx) installed on my car, so I've been able to monitor a lot of things that's going on behind the scenes in the car.

I periodically check my battery voltage and when I normally run my car, the voltage was around 14.4v to 14.7v all the time. But now for some reason, now, it's always at around 13.3v to 13.9v. Even when I run/accelerate the car, its only at 13.3v. Before when I would accelerate on my car, the voltage would go up. Sometimes even up to 15v+. But now, under acceleration, the voltage seems to be not affected at all. But when I hit the brakes and the efficient dynamics blue bar fills up on the dashboard, the voltage jumps back up to 14.7v during the time the blue bar is active. I assume this is the system charging the battery?

When I am idle at a stoplight, the voltage drops to about 13.0v. It used to hover higher, at around 14.3v. Also, when coming to a stop, just at the point when the car stops, the voltage would drop to about 12.5v and the car would shudder for a very quick second. I've never noticed this before as well.

I normally drive with my start/stop system off but decided to give it a try today and that's when I noticed the battery voltages not being the same as what I used to see. Also, when I would normally see the 14.7v voltage, I would only drive my car about once a week. Lately, I've been driving my car everyday. Could it be that my battery was getting drained back in the day and hence why my car always registered 14.7v as the car was constantly charging my battery? Now that I drive it everyday, the battery's got more juice and thus the constant 13.3v?

I'm not battery expert and I know most people don't normally monitor their voltage of the battery while driving but I'm wondering if this is normal? Could there be something up with my battery or alternator/charging system? On my other cars, I know anything in the 13v range denotes a healthy battery but I an unfamiliar with the battery specs for the F10. I am most puzzled with the fact that the car's voltage used to be at 14.7v when running and now it's suddenly dropped to about 13.3v.

Theres a reason most manufacturers either don't include voltage gauges in the vehicles, or use dummy gauges with a range basically showing "you're stuck on the side of the road", "ok" and "your car is about to melt". There are so many variances in voltage, resistance, temperature etc between not only the battery, but also the alternator. Basically anything over 13 volts when the car is running is fine as that means the battery is charging (technically anything over 12.7 is passable, but anything under 13 and I start looking for current draws, or I will explain more on that later). Obviously in a perfect world, everyone would like to see 13.5-14ish when at idle, but with the electronics load on the BMW, especially in the summer time, that will be rare. When the car is resting, anything over about 11.8 is fine while ideally you want 12.3-12.5 or so. This is the actual capacity of the battery, which is why every time you stop, you see it drop to that because the alternator is no longer charging it (obviously because it isn't moving). A battery in good working order should be able to start the car with anything over mid 11s in voltage, but a lot varies on compression ratio, external temp, battery temp, battery age etc, but if you consistently see your battery below 12 volts with the engine off, its either time for a replacement of the battery, the charging system is suffering (alternator), or you have high resistance in your cables (common in the high salt states and humid areas).

Now some quick alternator knowledge that will explain the high variance in voltage. Everything electric sucks power from the alternator... unloaded most will output 14.5-14.7 volts, however the more draw on the alternator, the lower the output voltage. The big current draws on most vehicles are the engine cooling fans, air conditioning, audio system, and obviously engine electronics/PCM. In the summer time you are almost always running the fan, air conditioning at a higher speed, often the seat coolers, stereo system, probably charging a cell phone, running the engine as well as trying to charge the battery which is used frequently to start the car. In addition in the summer time, the engine gets hot, the car gets hot, and typically the battery gets hot, which reduces output of it. When all those cables and connectors get super hot, it raises the resistance value as well, which translates into voltage loss. You could likely put a meter on the battery, alternator, and then watch your gauge and see 3 different voltages... of course thats all completely normal.

If this all still really bugs you, also realize your gauge is likely WAY down the chain where it actually meters voltage... put a meter directly on the back of the alternator and watch it, you will likely see higher voltage... also try it with all your accessories off and the engine cold to see how much higher it reads. Could it be a bad alternator? Sure... could also be a battery issue, but likely its just fine and you're seeing the summer load on the car, when it cools off I'm sure it will be higher again.

[lsturbointeg]

Good info FenixMike! I was about to mention what u said at the end paragraph about the gauge is down at the end of the circuit probably and if u want a true reading taking a multimeter and taking readings off the battery but u wouldn't be able to do that when ur driving LOL! But u can at idle and compare what ur gauge says to what the multimeter says.

[thealbert]

Originally Posted by FenixMike

Theres a reason most manufacturers either don't include voltage gauges in the vehicles, or use dummy gauges with a range basically showing "you're stuck on the side of the road", "ok" and "your car is about to melt". There are so many variances in voltage, resistance, temperature etc between not only the battery, but also the alternator. Basically anything over 13 volts when the car is running is fine as that means the battery is charging (technically anything over 12.7 is passable, but anything under 13 and I start looking for current draws, or I will explain more on that later). Obviously in a perfect world, everyone would like to see 13.5-14ish when at idle, but with the electronics load on the BMW, especially in the summer time, that will be rare. When the car is resting, anything over about 11.8 is fine while ideally you want 12.3-12.5 or so. This is the actual capacity of the battery, which is why every time you stop, you see it drop to that because the alternator is no longer charging it (obviously because it isn't moving). A battery in good working order should be able to start the car with anything over mid 11s in voltage, but a lot varies on compression ratio, external temp, battery temp, battery age etc, but if you consistently see your battery below 12 volts with the engine off, its either time for a replacement of the battery, the charging system is suffering (alternator), or you have high resistance in your cables (common in the high salt states and humid areas).

Now some quick alternator knowledge that will explain the high variance in voltage. Everything electric sucks power from the alternator... unloaded most will output 14.5-14.7 volts, however the more draw on the alternator, the lower the output voltage. The big current draws on most vehicles are the engine cooling fans, air conditioning, audio system, and obviously engine electronics/PCM. In the summer time you are almost always running the fan, air conditioning at a higher speed, often the seat coolers, stereo system, probably charging a cell phone, running the engine as well as trying to charge the battery which is used frequently to start the car. In addition in the summer time, the engine gets hot, the car gets hot, and typically the battery gets hot, which reduces output of it. When all those cables and connectors get super hot, it raises the resistance value as well, which translates into voltage loss. You could likely put a meter on the battery, alternator, and then watch your gauge and see 3 different voltages... of course thats all completely normal.

If this all still really bugs you, also realize your gauge is likely WAY down the chain where it actually meters voltage... put a meter directly on the back of the alternator and watch it, you will likely see higher voltage... also try it with all your accessories off and the engine cold to see how much higher it reads. Could it be a bad alternator? Sure... could also be a battery issue, but likely its just fine and you're seeing the summer load on the car, when it cools off I'm sure it will be higher again.

Thank you very much for the info! It was very helpful and explained a lot. Looks like everything is good with my car. Thanks again!