Have 1998 ML320
Vehicle would not start, dead Battery. Called MB roadside servive and they came checked battery said it needed replaced and did so. Now it will start ,run for less than a second and die. continues to do same. Roadside tech has no clue. Any suggestions on what the problem could be.

If by any chance you have a voltage meter.Check your new battery to see if it has at least 10.5 volts. If it doesnt the car will not start or it will and only run for a brief second. Sometimes new batteries aren't full. But all new Benz batteries come with a two year warranty.Hope it works out for you.

What are your fuel pressure and quantity measurements? Check for a clogged fuel filter by removing it from the vehicle and draining the fuel out of the filter. Then blow through it in the direction of fuel flow. You should be able to do so with little resistance if not clogged.

Might be an ignition key 'authorisation' problem (i think the system is called 'DAS'...'driver authorisation system', try any of your spare key(s) to start the engine first....before spending $$

i would hope the tech would know better, but i have seen many mercedes Ml's develop this problem, at the shop were i work we have seen quite a few with this, and it always has occured either during jump starting or while replacing the battery. what appears to happens is if the key was on or even in the ignition when the battery was replaced or while jumper cables are connected, it appears that the voltage spike that occurs during this action some how removes the key from the programming in the AAM and renders it useless, i have seen some that when a new key was used it will start, and on others the key and the all activity module has to be replaced. before you go too much further you might try another key.