Battery Charge/Discharge Testing
The ePure battery is rated at 1875 watt-hours and nominally 50.4 volts.
The discharge test was conducted at a constant 10.0A rate. This rate was easy for me to achieve and is reasonably representative of the average current draw while free-riding. Interestingly, this equates to an average power delivery of well under 1 horsepower.
The discharge took 187.75 minutes and the battery yielded 1610 watt-hours. This is obviously less than the battery's rated capacity. It's likely that withdrawing energy at a slower rate, or intermittently, would yield more energy. Conversely, withdrawing energy at a faster rate would yield less energy.
When recharging the battery, it accepted 1823 watt-hours from the DC side of the charger. Some of this energy is wasted as heat by the internal BMS performing cell balancing.
The energy required from the AC line was 1953 watt-hours. This equates to a charger efficiency of better than 93%. However, the power factor is far from unity. I measured the 5.7's charger at 0.66 (leading) with a Fluke 39. This is representative of a typical non-power-factor-corrected off-line switched-mode power supply (e.g. desktop computer).
Interestingly, it took about the same time to charge the battery (180 minutes) as it did to discharge it.
The charger initially operates in a constant-current mode (at 15.5A) until it reaches a battery voltage of about 58 volts. This period is when the lion's share of the energy gets transferred (taking about 100 minutes). The charger then operates in constant-voltage mode until the battery reaches about 58.7 volts.
After charging is complete, the charger's fan turns off and it enters maintenance mode, delivering about 0.83A (50W) to the battery. I don't know how long this might continue. Possibly indefinitely? It's possible the BMS would consider cell temperature and open the charging relay. The charger itself continues to draw about 13 watts after it is disconnected (unplugged) from the battery.
The spreadsheet on left is the discharge test. The spreadsheet on the right is the charge test.