The battery pack itself is rated at 1.17845 kWh. Each of the 13 cells is rated 90.65 Wh. At some point, Kokam may have had a US presence, but it appears to have been acquired by SolarEdge back in 2018.
Physically, this is a very large relay - often called a contactor. It likely also contains a precharge resistor for the motor controller. A note in the Kelly User Guide says, “All contactors or circuit breakers in the B+ line must have precharge resistors across their contacts. Lack of even one of these precharge resistors may severely damage the controller at switch-on.” Kelly specifies the precharge resistor as being 1k ohm at 10 watts.
This appears to be the only component in the enclosure with a country of origin label. It says Made in Korea.
Hall-Effect Current Sensor
The current sensor is a blue toroid. Both the charge and the discharge wires run through it. Using a Hall effect sensor does not waste any power in a current shunt (although it does require a small source of power for the signal-conditioning electronics).
The SoC indicator appears to be nothing more than a special LED voltmeter (which would explain why it is so non-linear). It seems quite similar to the ones used for lead-acid batteries sold on Amazon.
From the 5.7's Owners Manual, “Only when the battery is fully charged will the 10th LED (far right) be lighted. As the battery’s state of charge decreases, successive LEDs light up, one at a time. When the 2nd (from left) LED flashes, this indicates 'energy reserve'. When both 1st and 2nd LED flash, this indicates 'empty' and a new battery is needed to replace the old one.”
This is a simple SPST switch. It applies power to both the BMS and SoC indicator. Honestly, it is a very poor quality switch (and it's installed upside down compared to a normal residential light switch in which the lever is flipped up to turn on the light). I expect to have to replace it eventually.
The charging port is similar to the 3-pin XLR used in professional audio work, but it is keyed slightly differently. These connectors are typically rated for a maximum of 16 amps.
The discharge cable conductor is 25 mm² wire, which is approximately equivalent to a #3 AWG. It has a resistance of 0.222 ohms per 1000 feet (222 micro-ohms per foot). It is rated to continuously carry about 150 amps at 30 degrees C.
Assuming a 150 amp load, the voltage loss is about 33 millivolts per foot (by E = I * R). The self-heating (power loss) is about 5 watts per foot (by P = I² * R).
The power connector is equivalent to an Anderson SB-120 which has an average mated contact resistance of under 0.136 milliohms (which includes 5.5 inches of #2 AWG wire).