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Update - Went out and bought a Bosch AGM Glass Mat Battery (850ccca) and it set me back $330. Swapped it out and out of the Box, the voltage on the new battery read 12.0-12/1V. Started the car, and drove 2.3 miles and sure enough it happened again. Heat to red, Rpm, speedometer, odometer, economy gauge, all stopped working and car went limp while at a stop. No trans failsafe yet but it came on about 1 mile down the road. ABS and Brake lights were both on, but no service engine until the Trans failsafe came on.

So now I have a new battery, a genuine Bosch reman alternator that was put in 14 months ago and it charges at 13.6V pretty much constant and the same problem. Any other thoughts would be appreciated!

'Get the code read. Lights don't come on for no reasons.

I gave up... took the car to an indy and he scanned and said there were errors in the DME and communications errors with the CAN. I have to take it back next week and leave it for a few days but I am really bothered by that fact that it hasn't been solvable... I'll update once I know more.

This is not to knock you when you're in the midst of figuring out what's going on with your X5...but if I may...I'd like to use your post as an example for all the recent "battery replacement" threads.

As mentioned of late in the replacement battery threads...there are multiple brands that work...and one should look for a 49/H8 or 95/H9 battery class size. You also have the regular lead-acid battery or AGM (glass mat) types to choose from.

There are only a few major battery manufacturers that make most of the battery brands sold...and there's also a few "boutique" battery mfgs out there as well. The prices of these batteries run from relatively low (around $100) up to around what you paid ($330)...depending on if you're looking at a lead-acid battery or an AGM (absorbant glass mat) battery.

For example, your Bosch AGM battery (which sounds like it's probably an H8 battery size) cost $330...where as the Autozone Duralast H8 Platinum (also an AGM battery) has the same specs...and are mfg'd by the same company (Johnson Controls) and usually costs approx $170-$180. It has a 3 yr free replacement warranty:

• 170 - Reserve Capacity (minutes)
• 975 - Cold Amps
• 850 - Cold Cranking Amps
• _92 - Amp Hours

I would try and clean ANY connector's you can find with WD-40. My car had the same problem but did no dash lights came on, just trans fail. I cleaned the two connectors that plug into the trans and it fixed it permanently.

All you do is pull apart the connection plug and spray WD-40 in both sides of the plug and plug it back together...do that to any harness you can find for trans and alt..

Not saying it will fix but fixed mine. If the connectors are corroded it will do the same thing. Check the ones at the trans first.

I'm still thinking it's your alternator. Remans failing early isn't anything new.

Even a 1 second spike or drop in voltage can cause all the lights to come on. Then after the car sits for a bit, you start it and they are gone. Until the next drop/spike, then they all come on again.

FYI--Never rush to buy parts--troubleshoot, troubleshoot. While after the fact, a conclusive battery test is a load test that most auto parts stores will do no charge.

The reason for suggestions to check the charging system is that BMWs are very sensitive to voltage that is less or greater than specs.

I agree that the problem may be the alternator but it could also be something else. While you are waiting to get it in to the Indy you could unlock the cluster and monitor the alternator output.

FYI--Never rush to buy parts--troubleshoot, troubleshoot. While after the fact, a conclusive battery test is a load test that most auto parts stores will do no charge.

The reason for suggestions to check the charging system is that BMWs are very sensitive to voltage that is less or greater than specs.

I agree that the problem may be the alternator but it could also be something else. While you are waiting to get it in to the Indy you could unlock the cluster and monitor the alternator output.

Thanks for the replies as they're greatly appreciated! I must say, now that I have battery 101 down thanks to the great clarification/breakdown by Qsilver7. I didn't know there were so limited manufactures producing the same thing with different labels on them.

As for the alternator, I too am skeptical that the Bosch reman, even though is supposed to be superior to other might be spiking / dropping voltage for a split second. Upon unlocking the cluster though, it seems to hold steady around 13.5V +/- 0.1V. I took the car to my Indy for a quick diagnose and for him to read the codes the other day. Upon connecting it to the computer, there were 27 codes.. most were nonsense held in the memory form the past but he said there were three that were serious... If I remember correctly, CAN Communication error, Transmission Control module communication error, and another DME communication error.

He wiped the codes, restarted the car and sure enough within a few seconds the Christmas tree of lights in the dash came on again, gauges stopped working and temp gauge went to red. He basically said it looks like something more serious and that he'd need to spend a lot more time into looking at the cause of the errors. Dropped off the car this morning so I'll update this post on what his findings / corrective actions were. BTW - He showed me the transmission forward drum from another E53 owner who had driven ignoring the Trans Failsafe error. He said that basically due to lack of hydraulic pressure, the metal drum started to crack and the whole transmission had to be rebuilt. I've been super gentle w/ it during this time and only driven it if I had to, but needless to say it got my attention.

On a side note most likely not related to this issue but who knows really... , one of the error codes was for the thermostat. Now, I know that I had a brand new one replaced when I did the water pump about 20K miles ago, but I don't understand what could be causing it. The mechanic said your fuel consumption with go down the drain since the car thinks it's colder than it really is and will dump more fuel. My OBC says I average about 11.7MPG in normal mixed city / freeway driving. Does that sound about right? Probably meant for another thread but if anyone has a quick answer, I'd appreciate it.