Hi I have a 2009 ML 500 The battery went dead we recharged it. Now my stereo says device unavailable

The stereo is needing a code to put in before it will work. It should be in the owners manual. If not, you will have to check with a dealer who may provide a code for a small fee. You will need proof of ownership of the car.

replace a new battery.
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WiFi OBD device

Your battery is most likely dead if your lights go out. Charge or change your battery, but your altenater maybe be bad. It recharges your battery, if it don't work your battery will die..

This is because when the battery went dead it lost the programming. I would look in you user manual on the steps to program the phone.

When inside your car is it a the IBS (intelligent batery sensor) what this is the all recharging controlls. Battery must a registrated to car memory when new is where after change to empty battery! In diagnostical tools only! Car remember so how a old empty battery and recharging no good!

WARNING: Use you AGM specially batterie with fibre glass for your BMW attached only!

the stereo may have connection with your anti theft device, drive your car to the dealer and they can reset the device for you at a minimal charge. this should resolve these issues. Good luck

is there any lights in the led? sometimes radio needs to be re-coded...

alot of newer cars have an anti theft system for the radio and when you lose power you have to enter a code into the radio so you may have to call the dealership to get it

hi.there...i hope it's not too late to give you solution about your problem....
after i reading your problem i think the main problem is at your battery car condition...did you know every battery car have a life time even if you use a dry cell battery... if you already try to recharge it twice but it's only work only for two or three days..that's mean you must replace the battery with the new one.. just make sure when your repalce with new battery it must same type with the factory recomenned (ex: NS 70 ZL or else ).
after your replace with new battery car with new one you can add car stereo tape that what you want but still you must be carefully with cable installation.just give it to the expert one.
the life time for the car battery is usually (if you use standart application) is about 1- 2 years. more longer if you use dry cell battery the life time is around 3 yaers but the price is more expensive for the dry cell battery....