2004 ML350 - electrical gremlin & other matters

[Gil]

Got a 2004 ML350 with 92k on the clock. Been a decent vehicle so far, only one major repair (cracked intake manifold - $1500 bucks).

Of late, there is a persistent problem with the car battery dying if left undriven for more than a few days. My mechanic thought it was a bad ground and fixed one area that looked like it could be the fault (a rusted ground, he said), but this did not help. The battery was replaced not even a year ago; I keep the car on a trickle charger while in the garage but it's very frustrating to have to wonder about this every time I need to leave the car unplugged somewhere for more than a day.

The little wrench shows up in the dash now, with "1200" next to it - I presume this is a reminder for regular service intervals; I'm about to take it in for plugs & wires anyway (thought about doing this myself but there seems to be a lot of horror stories about removing plugs on these engines).

Also, the check engine light is on (code reads P0446; charcoal canister troubles, according to many others)

Any thoughts or other suggestions are much appreciated, thanks.