[JRMichler]

This problem does not have a closed form solution. You need to calculate the number of stops for a range of speeds, then the driving time for each speed, and add in the recharge time.

Let's start simple, then decide if we want more detail later. Assume start with 100% charge, on the road quick charges to 80%, and stop for recharge at 10%. That gives 90% range with the initial charge, and 70% range with on the road charges. Now calculate range vs speed, and number of stops for these numbers:

Speed 90%range 70%range Number stops
50 ... 335 ... 260 ... 3
54 ... 297 ... 231 ... 3
55 ... 290 ... 225 ... 4
60 ... 250 ... 195 ... 4
100 ... 103 ... 80 ... 12

Figure 45 minutes for each recharge.
Speed DrvTim ChrgTim Total Time
50 ... 20.0 ... 2.25 ... 22.25 hours
54 ... 18.5 ... 2.25 ... 20.8
55 ... 18.2 ... 3.00 ... 21.2
60 ... 16.7 ... 3.00 ... 19.7
100 ... 10.0 ... 9.00 ... 19.0

Somebody else can fill in the numbers for speeds between 60 MPH and 100 MPH. The optimal speeds are those which get to the destination with only 10% charge left. Go slightly faster, and you gain minimal driving time, but need one more charge. So 54 MPH is the best speed for three recharges on the road because going 1 MPH faster requires one more recharge.