BMWNA also told me to use either a trickle charger or battery tender. Not just my dealer.

Craig

Not true. The starting systems of most vehicles have capacitors which increase the amperage of the 12v battery within the X5.

10-mins. will replace what is used.

It's same technology that's used in a stun gun, whereby a 12v battery, only powerful enough for a smoke alarm, can incapacitate a large human, in fact a few dozen large humans, before requiring replacement.

Steady driving, at a steady speed, will kick the alternator on, hence charging the battery. At idle, the alternator may not be charging the battery.

I have owned my 35d for less than one month. I do not know what RPM range that BMW set the alternator to kick-in at.

I'm by no means suggesting one idles their 35d in their driveway, I was merely using that as an example to demonstrate that the car does not know if it's being driven or simply idling high, nor should the alternator care.

The reason the alternator does not operate or draw a load from the engine below a certain RPM is to allow the engine to idle smoothly. If the alternator were drawing a load from the engine at 600 rpm, it would be putting much more stress on the engine, creating a rougher idle.

Customers demand vibration free idles, these days, hence most cars run strictly off their batteries at idle, with some exceptions.

Anyway, if a battery tender is needed, what's the big deal. You guys are operating your X5s in some pretty harsh climates, and it's a $30.00 purchase.

If it bothers you that much, just buy Optima 12 Volt Performance Battery - Sealed Batteries by Optima an Optima battery and call it a day. There's no harm in spending $150.00. I'd spend that just to avoid having to take my X5 into the shop. The time and annoyance is worth far more than $150.000.

So what if BMW equipped their X5s with crappy batteries. Big Deal. It's pretty minor, and there are no perfect cars out there. Every car has it's bugs.

Going back to my secondary vehicle: my Honda Civic, it's 1-year old with 27k miles on it, and it left me stranded in a parking lot the other day due to a dead battery, probably caused by the fact that I park it outdoors in the 40-degree Bay Area winter weather.

Solution: Optima 12 Volt Performance Battery - Sealed Batteries by Optima

I had a red top Optima in my Infiniti QX4. I never had to plug a battery tender on it, or any other vehicle I've owned. I did have one on a Harley Davidson motorcycle, but it wasn't used much and was installed by the Harley dealer before I took delivery...

Craig

ABMW:-

10 mins running (at any RPM) will not replace the discharge caused by one start. There are no capacitors in a vehicle starting system.

A bigger battery will not help if the running time in insufficient to charge the battery.



90% of the info you have posted above is just plain wrong, maybe you would like to post some links to support your capacitor statement for instance.??

Sorry, but that statement makes no sense whatsoever.

Capacitors are built into many starter motors within automobiles today. They assist in the initial rotations of the motor. If BMW left this out from their design, so be it. But, many companies use this technology and if anything that bit of my thread is incorrect.

As to 90% of my thread being incorrect, I beg to differ. But, this is about solving a problem with our cars, not between your knowledge bank vs. my knowledge bank.

As to 10 mins. of alternator charging not being enough to recharge the energy taken from the battery during one (1) start cycle, that info is entirely incorrect.

Do you believe one must run their vehicle for 30-mins. in order to recharge their batteries to the state that they were at prior to 1-start cycle? That's only the case, if the battery were on the verge of discharge-in the first place.

A healthy battery should need no more than 10-mins. of run time/charging from an alternator in order to recapture any lost capacity from starting an X5.

"Trickle Charing" is FAR different than the "Peak Charging" that takes place when a vehicle is running. A trickle charger could take hours to replace what peak charging can perform in minutes.

You're free to google the terms I've used. There's no need for me to do the work for you. I've already provided you with the information here. This is first source info.

I'm factually aware that it's on google, as it's widely known, to anyone who is in the battery or electricity storage industry. But, with due respect, I am not wrong.

I will admit that I am new to BMWs and their starters may not use capacitors. So if they don't I will retract that individual statement, but that's the limit of my apparent misinformation.

No, they are not.

Capacitors are used on AC motors, not on DC motors. An automotive starter is a DC motor.

If you are thinking that the lump on some starter motors which looks similar to the capacitors on large AC motors, it is not -- the lump is the starter solenoid.

Do you have a link or reference to capacitors being built into engine starter motors? If so, I will gladly admit I am in error. But in 44 years of working on engines, I have never seen a starter motor on any engine which used a capacitor.

That's absurd. I've parked 3 different X5's outside 24x7 in the NY/NJ weather since '01 (and '01, '04 and '08) and if 40* weather for a year causes a battery to die there would be a big business in battery jumping in the area, which there isn't.

So, did it start? Because I've heard that 40* weather can really kill a battery :bustingup

I think there is some confusion. In ALL electronic modules used in any vehicle, there are capacitors called "mov's" which have the sole purpose of protecting modules against surge currents when the starter is cranking. During the crank cycle, its at this point where the harshest spikes are generated. You'll note that when you crank, nearly everything goes dead during the crank and then come alive once started.