charger voltage you can measure with the voltmeter probes directly off the black and red wires, while the charger is charging, or each end of the battery because the entire battery is pushed to that voltage while charging.
a shunt is a super low resistance resistor which is placed in the current path so that there is a voltage drop across the shunt according to ohms law. V=IR. this voltage is then fed into a meter to display it, as in the case of an ammeter, so that you can measure a large current in a large conductor without running the current through the meter, which would blow up if large currents went through it's small wires.
in controllers and these battery management systems, BMS, the current flowing out of the battery goes through a shunt made up of several large short bare wires soldered in line with the current path on the board, together besides one another close to the output. the BMS compares the voltage across the shunt to a reference voltage it creates from a zener diode and a resistor divider to establish the maximum voltage allowed across the shunt before the comparator (an active device essentially like an op amp, which has the shunt voltage and reference voltage as inputs) turns off the output FETs, causing current flow out of the battery to cease. so when the current is too high, that voltage drop becomes so large that the BMS knows to shut down.
in controllers, people add solder to fill in between the shunt wires, or additional wires in parallel with the shunt wires, to lower the shunt resistance, so that it takes a larger current flowing through the modified shunt resistor to cause the comparator to shut down the controller.
people also have done this to the BMS on some battery packs, in order to force more current from the packs under demand. this is usually done when the battery is small and the current that is needed is larger than can be supplied by the factory shunt setting.
you can see a lot of references to the shunt solder modification in various threads, but i think it started in the original crystallite controller modification thread.
you can put 2 packs in parallel and get twice the current like you said but then in your case the maximum current would be on the order of almost 200 amps at 5C times 58V is about 12kW, and that is more than even 8AWG can safely carry, except for a few minutes. you could still get the same power by arranging the packs in series, and raising the potential to 96V nominal, 115V fresh off the charger. people are currently trying to hack together controllers which will run at these voltages, since the Kelly controllers which operate at those voltages are pretty costly. the important thing about voltage is the way that brush less motors work, and the ultimate speed of the motor is a function of the voltage, and the torque (the 'strength' or push) is related to current. all motors have a voltage konstant, called K, so that Kv determines the ultimate motor speed. make sense?
when current flows through wires, there is a voltage drop along the wire which is directly related to the current flow, and heating of the wires (in the wiring harness and the motor also) follows current squared, so higher voltage is better because the power losses are lower, just that the technical problems of operating at higher voltages is more work, but that is where it is gonna go as more controllers get hacked up to run up there.
steveo is doing some real pushing of the boundaries there, and there is a thread on the 18FET infineon controller which people want to run up there and be able to handle 200A loads. it requires using higher voltage capacitors, and output driver FETs able to withstand the higher voltages, along with modifications to the circuitry to allow the internal circuits that supply current from the battery, for the pcb logic voltages down to usable levels for the logic circuitry to work at, from the higher voltages, by dropping the maximum voltage input to the voltage regulator that supplies current to the logic circuits on the pcb. that is what knuckles, phil, and geoff are doing on the infineon controller thread. hope this helps, they really are doing good stuff inside all that gobbledeegook.
