Voltage and Current work hand-in-hand to determine Power like the basic Power formula of P=V*I. You can have a Voltage source with varying degrees of Current (amperage) capability. A simple example is an AAA, AA, C, and D-sized battery cell that powers things like remotes, flashlights, etc. Think of them as mini DC chargers. Although each is a different physical size, each size has the same output Voltage level of 1.5V but each has a different maximum Current output capacity which also means it has a different Power output capacity. A 1.5V D cell battery has a much greater Power/Current output capacity than a 1.5V AAA cell battery....both same voltage. Unless running across an "old" DC charger limited to around 400-500V the sDC charger you find now days will have an upper voltage rating around 900-1000V (probably closer to 950-1000) whether it's a 50KW, 120KW, 180KW, 360KW, 720KW, etc., DC charger. Nothing really special about that voltage rating. Well, if they all have the same upper output voltage level capability why can the 720KW charger put out a ton more power than the 120KW charger....the answer is greater current output capability. Yes, high power lines feeding power across an area will be at a HIGH "voltage" because much smaller in physical size/weight lines are required compared to lines required to carry HIGH "current/amps." Generating "high voltage" is much easier than generating "high current"...and also requires much smaller conductors. Heck, we can drag our feet along a carpet and build-up static electricity on our body of up to approx 10,000V and when touching a door knob we'll see a mini lightning bolt jump between our hand and door knob to get a zap!!!!....a 10 kilovolts zap that although very high voltage but which has very little current/power capacity....our hand is not vaporized due to little current capability in the 10K volt static voltage charge. Also, those voltage levels for the SL7 and Tesla batteries represent their "nominal" voltage which is 3.2V for each LFP cell times the number cells. To fully charge an LFP cell it requires 3.65V. So in a SL7 battery with a 550V nominal voltage that means it has 172 blade battery cells. 172 cells x 3.2V = 550V. However, to fully charge those 172 cells (all in series) the DC charger will need to output up to 628V (3.65x172=628).....a voltage far below the 900-100V capability of the DC charger. However, unless that DC charger also has the current (amps) capability to provide the BMS EV battery requested current level of X-amps and volts, the power output will fall short since voltage and current must work hand-in-hand to provide power. Additionally, you can have two identically sized EV batteries....say two 100KW batteries and each could have a different "max/peak" charging rate and completely different 0-100% SOC charging curves depending on battery design/chemistry. While both will charge to 100KW, one battery might take 1 hour while the other 2 hours....each requesting different levels of power during the charging process. During the DC charging process the DC charger and EV BMS constantly communicate with each other like the DC charger tells the EV the maximum voltage & current (a.k.a. power) it can provide AND the BMS requesting a certain power level....both come to an agreement as to what power level actually ends-up flowing. That is, the charger "will/can not" provide more than a certain amount of power and the EV BMS agrees not to request more than that. If while charging the DC charger's output capability increases (like an EV sharing the charger finishing charging) then the DC charger BMS tells the EV BMS it can now provide more power if still needed and does the BMS want it?....the BMS will respond with a yes or no depending on its SOC charging curve requirements. Anyway, voltage and current go hand-in-hand for power. Increasing or decreasing either results in a increase or decrease of power. However, an EV charging system is design such as whether its a 400V or 800V charging architecture, max/peak charging capability, charging curve, etc., is another story in itself.
