second Battery 08 BMW X5?

[Chipmunk2k3 10+ year member]

I just learned that I may not be able to add a second battery to my 2008 X5.

Apparently the regulator is computer-controlled on the X5 and adding a second battery will screw up modules or something.

Does anybody have any idea if this is true and if there's a way to work around it? I've already purchased two DEKA AGM group 31 batts 100ah 925CCA to power old school kicker 2500.1 and 700.5

the x5 comes stock with a 180 amp alternator and a 90ah 950CCA group 49 battery. I've been running a Massive nx4, n2 and n4 for months with a little dimming but no other issues. Daily driver and gains are set conservatively.

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[Chipmunk2k3 10+ year member]

Anyone?

I'm not into competition or anything and I drive the car once or twice a week. After reading a few posts I'm thinking about doing a bank of ultra caps but I'm not sure if that will also have a negative effect on the X5.

 

[fasfocus00 5,000+ posts]

i'm pretty sure you have 2 batteries in that car. last one i worked on did.

 

[Chipmunk2k3 10+ year member]

i'm pretty sure you have 2 batteries in that car. last one i worked on did.

I'm only aware of the battery in the left side floor of the cargo area. Where is the other battery located?

 

[garychoffmann 10+ year member]

X5's have sketchy electrical. If you start having problems with your a/c specifically your final stage resistor run. BMW used some inadequate power runs in the x5. I don't know if I'd attempt modifying the charging system too much. I don't see how an extra battery could effect it too much but I would consult a bmw tech, or the bmw boards

 

[fasfocus00 5,000+ posts]

I'm only aware of the battery in the left side floor of the cargo area. Where is the other battery located?

there should be one under the hood near the fire wall, usually has some cover panels over it located near the firewall. the second is in the cargo area as you said. there should be a 2 gauge wire running from the front battery to the rear battery. I'd start with replacing both of those batteries to a good AGM battery.

 

[Chipmunk2k3 10+ year member]

there should be one under the hood near the fire wall, usually has some cover panels over it located near the firewall. the second is in the cargo area as you said. there should be a 2 gauge wire running from the front battery to the rear battery. I'd start with replacing both of those batteries to a good AGM battery.

Unfortunately no underhood battery in my X5. I disconnected the rear battery and there was no voltage in the line.

 

[fasfocus00 5,000+ posts]

Unfortunately no underhood battery in my X5. I disconnected the rear battery and there was no voltage in the line.

was the key put to on position? OEM battery isolator, the rear battery is meant to run all interior electronics and the front is meant to run all engine control electronics. I don't get many BMWs in but all the recent ones (2002-present) have had 2 batteries.

 

[Chipmunk2k3 10+ year member]

was the key put to on position? OEM battery isolator, the rear battery is meant to run all interior electronics and the front is meant to run all engine control electronics. I don't get many BMWs in but all the recent ones (2002-present) have had 2 batteries.

Doh!!! No it wasn't. I'll try that when I get home. I'm aware of a similar situation with the Benz ML which has the aux batt under the driver seat. Thanks

I pm'd Mylows to see if an HO alt is available.