Even with a new voltage regulator, I think with that kind of full load you can expect to see a voltage drop of some level. Generally as long as it doesn't drop below 12.6 when the engine is above idle I think you would be OK unless you do a lot of stop/go/sitting in traffic where the engine would be at idle, sitting at <12V. That will eventually kill the battery.

I upgraded my 190E's alternator to a 143 amp unit and have not had a power supply problem since. My 300D has a 150A unit as well.

Also you'll need a clamp-on ammeter to measure this level of current. Your meter can only do up to 10A.
http://www.amazon.com/Triplett-Clamp-On-Resistance-Temperature-Frequency/dp/B006GD0LC2

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