Michiganmike

My Battery Tender took a long time to fully charge the battery until I started placing a weight to close the switch on the passenger side of the engine compartment near the fire wall. This switch is normally closed when the hood is closed. However, when the hood is open the switch is normally open and my 535i does not appear to go into sleep mode. The resulting current drain with the hood open appears to increase the time to charge the battery. YMMV.

sc170

What do you guys think about this?

http://www.turnermotorsport.com/html...ID=82110026663

chalankanoa

I close the hood when using the battery tender. I just finished charging using a full size charger at 6A. The battery was initally at 95% charged and took about 2 hours to get to 100% charged. The indicator on the battery is still black, but its not an OEM battery it is an Interstate MTP-H9. I have not had any electrical problems, starts no problem. Maybe for the MTP-9H the indicator should be black? Checking the Interstate dealer website it states the colors are Green/Amber/Red. No mention of black.

Curmudgeon

Will your 535i go into sleep mode with the hood open and the battery tender NOT connected?.

Michiganmike

I do not know for certain. I suspect that the hood switch is there to keep some parts of system active whenever the hood is open. I first noticed this because of some low volume noises with the hood open. I saw the switch and wondered what it did. When I pressed it the noises stopped after a few seconds. I do not know whether there is a timer to activate sleep mode after a period of time with the hood open. Even with the switch closed there are occasional whirring or other noises, but not as frequent or sustained. However, I do know for my 535i it takes a few hours to fully charge the battery using the battery tender with the hood open and the switch closed, while it has taken more than two days to achieve full charge (as indicated by the steady green light on the battery tender) with the hood open and the switch open. My speculation is that there is a greater current drain for an extended period when the hood is open. I doubt that sleep mode status would change dependent upon whether or not the battery tender is connected.

My philosophy is to minimize deep discharge cycles in the hope that this may prolong battery life. Since my commute is under 5 miles driving alone may not keep the battery fully charged. The original battery in my 2003 530i was still going strong after 7 years when I traded it for my 535i.

Michiganmike

I do not know for certain. I suspect that the hood switch is there to keep some parts of system active whenever the hood is open. I first noticed this because of some low volume noises with the hood open. I saw the switch and wondered what it did. When I pressed it the noises stopped after a few seconds. I do not know whether there is a timer to activate sleep mode after a period of time with the hood open. Even with the switch closed there are occasional whirring or other noises, but not as frequent or sustained. However, I do know for my 535i it takes a few hours to fully charge the battery using the battery tender with the hood open and the switch closed, while it has taken more than two days to achieve full charge (as indicated by the steady green light on the battery tender) with the hood open and the switch open. My speculation is that there is a greater current drain for an extended period when the hood is open. I doubt that sleep mode status would change dependent upon whether or not the battery tender is connected.

My philosophy is to minimize deep discharge cycles in the hope that this may prolong battery life. Since my commute is under 5 miles driving alone may not keep the battery fully charged. The original battery in my 2003 530i was still going strong after 7 years when I traded it for my 535i.

NguyenAzn

i just bought a new battery too, so would you guys recommend me to connect the car up to the battery tender for it to maintain the battery ?

Curmudgeon

I believe the 535i has one. I had this same discussion with a 535i owner recently and that one did have a hood-up timer.

True. Until the sleep timer times out. One of the things that stays active is the fuel pump which you can hear release pressure when the car goes to sleep.

Agreed. I did not wish to imply that. We first have to establish that your car goes into sleep mode normally.

AchtungE60

To tell you the truth. Once your battery indicator is black, it's on his way out. I've gone through 5 different bmw's in my life and let me tell you...you cannot bring them back from the dead. It will even come back to green but it's a LIE! lol......do not believe and you'll notice this too. I have a trickle charger now and i stole it from my sportbike. Any 6volt/12volt trickle will work. It's just a trickle charger.