battery

A no start condition may develop due to an anti-theft system fault. If the drive authorization module fails to recognize the keys, the engine will not start. In many cases, a new module and keys will be needed to correct this problem.

You likely have a few problem going on at the same time. One might be the cause of the battery drain or not starting then your ML may have lost the key information. If it wouldn't start or it stop while driving but after say 30 minutes it would start and run normally then it might be your crank shaft position sensor. $50 sensor back of engine drivers side about 10 minutes to diy fix. It's one bolt and its right where the transmission bolts to the engine. Dealer will of course charge a weeee bit more to fix. If you can do it yourself it will save you a bit of cash. No adjustments or settings just one connector one bolt. A few videos on youtube on how to do it as well. Same engine M112 was used in quite a few Mercedes vehicles so as long as its the v6 the video shows how. I know there is one or two with the ML and that shows exactly how to do, just hard to find sometimes. If it was just starting then running about a second and shutting off then it may be your key. To check this put your key in the ignition and then look at your centre console. To the left side you should see a blinking red light. That means the security system recognizes a good key. It could possibly (rarely though) be your AAM (All Activity Module). Depending on when your 99 was built it may have the integrated AAM or if you are lucky the newer external AAM module. The integrated AAM is part of the general vehicle ECU and if that toast it can be rather expensive to fix. The external ones that normally start with 2000 or newer ML's (and some late 99s)is about $300-$800 depending on the source then programming etc at the dealer. A new key price is really depending on your dealer. You need to take the car you driver licence , registration with you to order. The key is made in Texas and shipped to the dealer. So if they didn't prove you were the owner they could be liable if someone ordered the key and stole your ML. I bought a new key last summer and it was about $350. Some people have said they get them for about half that and the odd one pays more and I have no idea why other than stealership greed. Takes about a week to get it in and can only be purchased at the dealer as the keys are laser machined and the fob include the rfid tag that the AAM reads when you insert the key. Usually takes about a half hour of dealer time to get the key recognized or added to the AAM. This can be another problem as in the early AAM's there are only 8 key slots. After they are full the usual practice is to replace the AAM. However if your dealer is a good one they can just reuse one the of the later slots for your key. And as a word of advice the resale value of your ML is higher with two working keys. You should have one of the FOB keys that lock and unlock the doors and turn off or on the alarm and at least a second key which if you want to cheap out get the valet key aka the mickey mouse key (it looks like his ears) That's about $150 and sometimes less. So you need to charge the battery and stick the key in, then look for the blinking light that will tell you if the AAM and key are good. If its blinking take a big sigh of relief. Then you can probably just look for the reason it won't start or run.

If you can't afford to repair the odd issue and carry out regular servicing, perhaps you should look @ a "Duster"?!