The cables between a battery and an inverter drop voltage in proportion to the current they carry and the resistance of the run. A longer run has more resistance. A heavier load pulls more current and the drop grows with it. The inverter then sees a lower voltage than the battery terminals do, and the battery sees a higher charge voltage than the inverter thinks it is applying, unless the manual's sense leads correct that error. The practical consequence is simple: when the manual's chart says the run is too long, put the inverter nearer the bank or use the conductor that chart allows. This page has no wire-size table.
Same power, half the current, as arithmetic
Power, voltage, and current are tied by P = V times I. For the same power, current is half when voltage is double. A 48 V bank therefore draws half the current of a 24 V bank at the same inverter power. That sentence is the arithmetic of the definition, using 24 and 48 as the two nominal bank voltages people compare. It is not a measurement of your cables, not a quote, and not a statement that every 48 V system runs cooler. Halving the current halves the drop only when the resistance stays the same, which means the same conductor and the same length. Change the cable and the drop changes again.
Why a designer picks 24 V or 48 V in the first place, including inverter availability and how many parallel strings of batteries the bank becomes, is in 24 V versus 48 V solar battery banks. Voltage drop is one term in that choice. It is not the whole choice. A 48 V bank with an undersized cable can drop more than a 24 V bank with the cable its own manual demanded.
Take a teaching pair, hypothetical and not a product. Suppose a load of 1,200 W. At 24 V the current is 50 A. At 48 V the current is 25 A. Those amperes are P divided by V, nothing more. They are not a breaker size and not a cable size. If the same cable drops 0.4 V at 25 A, the arithmetic of a resistive drop says it drops 0.8 V at 50 A. Whether 0.4 V or 0.8 V is acceptable is the manual's percentage or voltage limit, at the nominal voltage of that system. A tenth of a volt that is trivial on a high-voltage pack can be a serious fraction of a low-voltage bank. Insert your own power, your own voltage, and the chart in your manual. Discard these stand-in figures when you do.
Put the inverter where the chart still holds
People hide the inverter in a convenient room and run the battery cables the long way around a doorway. Every extra meter is extra resistance, and the high current at the low-voltage side makes that meter expensive in drop. The layout that respects the chart is usually the inverter close to the bank, with the longer run on the AC side, where the voltage is higher and the current for the same power is lower. AC drop is still real, and it has its own rules. It is simply a different number, calculated by the person who signs the electrical work, from the AC voltage and the AC conductor.
Loose lugs imitate a long cable. A joint that was never torqued to the value the lug requires adds resistance, heats, and sags the voltage under load. The voltage at the inverter then wanders with the load in a way a correct cable of that length would not. Checking torque is a qualified person's task on a live battery bus. An owner can notice that the inverter faults on low battery while a meter at the battery terminals, used by that qualified person, still shows an acceptable voltage. The difference between those two readings is the drop, including every dirty or loose joint in between.
Sense leads, if the manual offers them, measure voltage at the battery and let the charger compensate. They do not make a thin cable safe, and they do not remove heating in the cable. If the chart says the run is too long, sense leads are not the chapter that permits it. Shorten the run, or install the conductor the chart names for that length and that current. Charge stages that never quite reach the battery because of an uncompensated drop will slowly undercharge the bank, which looks like a tired battery and starts as a cable.
