[harmony_k15]

Sorry if this has been asked here before.

Bought our E91 (2006) and it had an awful aftermarket single DIN unit fitted.
Not only was it ancient but it lost memory after locking the car.

I fitted a Sony DSX-a410BT and this had the same problem.
After asking on the FB groups I was advised to piggyback off the fusebox.

I think I have tried every available slot and with all of them the unit loses its memory after the car is locked and left for 15mins-ish (Sleep mode?)

Failing this I went "old-school" and wired a fused line directly from the battery. The unit worked as it should, only on with the ignition on and held its memory.

Now when my wife tried to go to work this morning the battery was dead

Now on the FB pages more than one person has said they used this method and had no problems, is it likely that just having the glove box open all day yesterday will have drained the battery enough to cause starting issues?
For background, after getting tyres fitted yesterday morning the car had only driven appx 1 mile.

Any constructive help is appreciated, too many people on the FB group willing to troll without reading the post properly.

Thanks in advance.

[Sayek]

I removed the BMW CD player and fitted a single DIN MVH 280FD-Pioneer and also added the door tweeters. The sound was a huge improvement as the aftermarket had a better built-in amp.. could even hear some bass now

I also purchased the extra wire harness so the steering controls still operational.

Connected a thin cable direct to the battery with a inline fuse. It works same principle as your only with ignition on. Fitted it about 4 years ago and no battery issues.

[harmony_k15]

Thanks, it does seem that the dead battery was un-related.
My headunit is wired in the same as yours so shouldnt be causing issues.
Thanks for confirming this.

[Russbmw]

The question really is how is the headunit connected?

Not gonna lie, it's been a good few years since I messed about with aftermarket headunits, but do they still not require a permanent 12v+ supply as well as a switched 12v+supply?

From what you've said, the headunit 12v+ permanent supply wire has been connected to the CAR's switched 12v+ supply, and no permanent 12v+ is there at all?

If you connect solely a 12v+ to the battery (fair enough, if you're not comfortable poking around with a test probe or multimeter to find one in the car), that would have to be done to the permanent 12v wire of the headunit. You would then need to reconnect what seems to have been established as the swithced 12v car supply to the switched supply wire on the headunit wire, as this is what looks for a 12v supply to switch the headunit on with the ignition.

Just connecting a 12v permanent supply direct to the headunit without a switched supply also being connected would leave the headunit permanently powered - although I guess you could switch it off by pushing or holding the relevant button?

Personally, I'd just check out the wiring that is there already and do it properly with the right 12v+ and 12v+ switched supplies connected.

[harmony_k15]

Thanks for the response.
You are right about the AM HU needing both a switched and permanent live, these are fitted correctly (Unit powers on/off with ignition).
As for the location etc, I have always preferred to leave wires intact and avoid splicing into them, just one less thing to go wrong and it means you can sell the car intact.
Since I posted this we have ruled out any power drain from the stereo and it looks like it was a combination of having tyres fitted and working on the car all day (lots of stop starts and short trips)
Can confirm on Sunday I reconnected the HU and took the car for a 160 mile drive to really get the charge back up and car has behaved fine since.

So TL;DR
Battery was drained by driving car on/off ramps at tyre fitter followed by my having the interior lights on for a full day.
Works fine now.
Thanks again for the response.

[sfarisminhas]

I've had three aftermarket headunits in my 2011 e90. I used a harness that generates a 12v switched signal. The constant wire either goes directly to the battery or to the fuse box. I plugged it into the slot that corresponds to the OBD. Never had a problem.