As you have a Super 7 I am tempted to say that now its running OK, go off and enjoy it rather than chasing down this voltage drop
If you do want to look further then I suggest you use the battery test option in PicoDiagnostics. This will test the battery and provide a value for the cold cranking amps (CCA). If the CCA is lower than the rating for the battery its probable that the battery is in poor condition.
If the rating is OK, then perhaps this is just normal for this vehicle as it probably has a tiny battery to save weight.
Well, as the temperature here i Sweden today is +12 degrees, i actually think i'll do as you suggest
Since the car is running fine (for now...), the problem could be considered solved and the thread closed!
Only problem for me now, is that the Pico is so interesting to play with that i just have to find something else to work on