[caz681]

I usually have my headlight switch in either the Auto or Off position, but I happened to have it in the Parking Lights position when putting the X3 to bed last night, and in my quick egress from the vehicle I did not notice the very helpful warning chime trying to alert me to the fact that I'd left the lights on. A surprised me found the X3 brightly lit in the garage the next morning, about 12 hours later.

Problems? None. Yes, there was a warning of excessive battery discharge and that some electronics had therefore been shut down, but the power lift gate operated with its usual vigor; and, most importantly, so did the starter. The warning of excessive battery discharge did not clear after my 10-minute drive to work, but I expect it will after a bit more driving brings the battery charge back up. I thought that I might have lost my radio station presets, but either that was not one of the things the computer shut down, or they are stored in NVRAM, because they were not lost. Everything seems normal.

So, I just thought I'd pass this on to anyone who was wondering how long the parking lights could be left on with a good battery. The answer is, at least 12 hours. This also makes me feel better about using the feature where you can leave the parking lights on one side of the vehicle lit when you street park it. Plenty of power for that.

[Alligator69]

On the other hand, get the battery fully recharged using a good quality (slow) recharger overnight, or over a several hours ride.

[April1]

Originally Posted by caz681

A surprised me found the X3 brightly lit in the garage the next morning, about 12 hours later.

Good information.

[Nahoa]

I'd appreciate your post except that you have only a ten minute drive to work . . .

[caz681]

Curiously enough, while the X3 was still warning me of excessive battery discharge when I parked it at the office in the morning, when I started it up at the end of the work day, the error cleared. Apparently it had actually absorbed electricity from neighboring cars during the day. Another indication of BMW supremacy. Poor suckers.

[DavC5000]

lol thats funny^^ hope you dont really believe it thou...

[RhoXS]

For whatever its worth, automotive batteries are not designed to be deep discharged and not designed to be left in anything other than a fully charged state at all times. In fact, they are designed only to provide a large amount of energy in a very short period of time and then be immediately recharged.

A deep discharge, like leaving the headlights on, is likely to permanently damage the battery to some extent. Yes, it will appear to fully recharge but it will also probably fail before it might have otherwise. This has to due with plates becomming soft when discharged and warping.

Also, leaving an automotive battery in an uncharged state, even slightly uncharged, for even a short period of time, will reduce the capacity of the battery. This might occur if one leaves something like a radar detector on even when the car is parked. The uncharged areas of the plates (sulfate deposits) will harden. These hardened areas cannot be reversed by charging. Therefore this will reduce the total plate area available to provide energy.

My only reason for stating the above is to make sure it is understood that it is certainly not inconsequential to leave lights on (even though it might immediately appear to be no problem) and heavily discharge an automotive battery. Marine batteries are designed to be deep discharged but they also require compromises that would not make them ideal for automotive use.

[caz681]

Lotus7?

[Earlofessex]

Originally Posted by caz681

Lotus7?

Lotus would respond with a good technical description of the new battery technology used in the F25, Efficient Dynamics, less frequent charging, etc. But, he's gone and I don't know nearly as much as he does. So, suffice it to say that this ain't your grandma's car battery. I wonder if heavy discharges have the same effect as on a traditional lead acid battery...

[RhoXS]

Originally Posted by Earlofessex

I wonder if heavy discharges have the same effect as on a traditional lead acid battery...

Very good question.

Since BMW is using their so called Brake Energy Regeneration system, the battery is not recharged after starting as quickly as it would be with a normal system and is probably not always kept fully charged. Unless the battery gets to some undefined low state of charge, the alternator only loads up when braking or decelerating. Therefore, I wonder if they are not using a battery that is designed similar to a marine battery that is intended to tolerate deep discharging.

It appears to me the system probably has more value for stop and go city driving but about zero value when mostly on cruise control, as is a high percentage of my driving. Therefore, I question if the Brake Energy Regeneration system saves enough gasoline to warrant the additional cost for having it, to say nothing of the extra complexity, weight, and potential repair costs.

BMW states "up to 3%" improvement in fuel efficiency which means, on the average, it is probably much less than 3%. I would guess even 1% is high in the real world but I will use 1% as follows. Assume 15,000 miles per year, 20 mpg, and $4.00/gallon. Then 1% of the cost of a years worth of gas is only $30.00. In my opinion the Brake Energy Regeneration system is more of a marketing gimmick than any real total cost saving device.

[caz681]

Actually, I was implying that RhoXS is Lotus7.

[Nahoa]

Thought the same. Would be glad to see him back, whatever name. Apologies to RhoXS for any slight in this, none intended.

[RhoXS]

I am not Lotus7 but no offense as it sounds like that might have been a compliment.