The Voltwatch is quite sensitive with little or no lag. What you are seeing is actual voltage depressions at the point your Voltwatch is plugged in. You are seeing the actual voltage drop that occurs for a millisecond or two every time you draw a gulp of currrent to drive the servos. There is a voltage drop somewhere between the battery and the point you plug in the Voltwatch. Small gage wiring in the switch harness or dirty switch contacts will agravate this indication. Your voltwatch is doing exactly what it is supposed to be doing and doing it well, it is telling you your installation would benifit by a better switch, larger gage wiring and/or a battery with less internal resistance or more peak current capacity.