The hardest part about EV racing is charging.    For optimal fast charging of a Tesla M3 EV between stages the battery needs to be at 52-55degC.  If the battery is cooler, Tesla divert up to 7KW of available charge capacity for battery heating (4KW for single motor version). 

The race driver needs to know and keep the battery temp above at least 52degC when planning to charge in order to charge at the maximum available rate from any charger.   This is especially important for remote location charging where charge rates 16KW and below are achievable.  Otherwise an actual charge rate of about 9KW is achieved (assuming battery is warm enough to accept this charge).  This is almost 50% less charge rate than expected and from standard room temperature of around 25degC it takes 30 minutes to heat battery at 7KW to 52+degC at which point the heating turns off and the full capacity of charger is fed to battery.      (All this is the same if supercharging at 250KW however most people won't notice the missing 7Kw being fed to heating)

Scanmytesla app gives the data required to monitor battery temps (and lots of other cool stuff) but needs to be mounted in convenient position for racing.   This mount is specifically designed to fit with the race monitoring electronics so not necessarily best option for general consumer.

The cheapest tablet at time of posting was a LENOVO - TAB M7 3rd GEN with dims 176.18(H) x 102.28(W) x 8.3(D).   This print is designed to fit that.  You will need a right angle micro USB adapter.   You will probably need to glue the edges on.

https://www.scanmytesla.com