While the battery shown below looks identical to the other I posted, it is, in fact, a newly built battery.  As a reminder, I need 4 of these in the car to get to my full pack and roughly 32kWh of capacity, which should be good for over 100 miles of real-world driving range.  They will be configured with 2 in series and 2 in parallel to reach the desired voltage and capacity.  Lithium-ion batteries are amazing in a lot of ways, but require careful management to ensure the best performance, safety, and longevity.  To that end, it's critical to have a battery management system (BMS), which measures and reports on the cell voltages and temperatures and makes some calculations based on that voltage and measured current over time (coulomb counting) to predict a State-of-Charge (SOC).  

The multimeter is displaying 170Vdc, half of the pack's total voltage at roughly 30% SOC. 

The BMS in my system is made up of cell monitoring units which measure voltage on each individual cell and provides the data over a CAN bus which is wired into the circular connector on the outside of the front plate.  I recently received the small display that pairs with the BMS system to provide some of the available data to the driver.  I was curious to see how it all worked, so I hooked it up and ran through the available screens... 

Overall, I'm really pleased with the display.  It's clean and simple with a single rotary button interface and displays the information I'm concerned about - i.e. State of Charge (SOC), Pack Voltage, Pack Current, Low cell voltage, High cell voltage, Average cell voltage, and pack temperatures.  It's an OLED display, so the brightness, viewing angle, and overall visibility is really nice.  

You can see the "master" BMS control unit in the background.  This is what aggregates the CAN bus data from the batteries and provides the output over serial to the display.  The BMS unit is highly configurable through their software, so I'll be able to map the output pins to the various functions needed to drive contactors relays, water pumps, etc... . 

My current plan is to mount this display in the center console above the stereo slot somewhere.  I've been searching the forums and blogs for ideas...!  Let me know if anyone has a suggestion...