Hi,

My 2008 GL450 would not unlock today. Tried with both the remote smart keys and also tried manually with the keys in the smart.
Should I call the Merc Roadside assistance or the dealer... Please advise ASAP...

Thanks

Good chance you have a dead battery. Let us know the outcome - good luck!

Dealer Service rep is on the way... Is dead battery covered under factory warranty?

It might be covered if you don't have more than 50K miles but batteries are usually treated similar to tires - they have a lifetime shorter than the car and are not treated the same for warranty purposes.
Maybe a circuit is stuck 'ON' and drained the battery. In that case, whatever caused the battery run down - presuming it isn't a switch YOU left on - might be replaced under warranty. In other words, if a switch did what it was supposed to (stayed on) then it wouldn't be covered. If it was supposed to turn off - and didn't - then warranty would cover (if it hadn't expired).