I don't believe I've ever read anything about checking voltage drop this way anywhere here before but this is how to locate the problem spot(s). By using an inline voltage meter you are adding another spot for error as well as only seeing that a problem exists but not where it's located at. Also when using a GGTS connection the meter doesn't fit plus you need to know the drop on the battery as well.
I never find any problems with where the battery makes contact but i also keep them clean 'cause either they shine or they don't, too easy.
Now where I do find the voltage loss is at some places that look to have no problem at all and that is the
threads were the tubes screw together.
Here is how measure for voltage drop. I set volt meter to 20 v dc scale and put the positive lead right on the fire button and the negative lead on the base of the atty, fire it and read the voltage. Once you see a high drop ( say .5v) you can move the leads to different tubes to find the bad spot(s).
Tonight I checked my DHX-TS with a 0.7 ohm atty and got a reading of .5+, I expected to find that the problem would be the switch but it was at the upper end of the telescope tube.
The fix: I tear it all down and scrub the threads with a tooth brush and Arm and Hammer baking soda and dry and re-assemble and re-check.
VD now is .9 - .16 which is about as good as can be expected from a telescoping ss
mod.
Here's a picture but I couldn't fire it and snap the picture.
Let me just add, with a 0.7 ohm load and a .5 volt loss the 20 watt vape turns into 15 watts (approx)
Note: picture is of MKB-TS and my good meter is at home