The one cell lead acid battery far left has one red cap for one cell to add electrolyte (acid) and made up of lead (Pb) plates (lead acid battery).

In the middle picture is a 3 cell battery with three white caps for three individual cells to add in electrolyte.

On the far right the battery pictured is a 6 cell battery with six yellow caps for 6 cells to add in electrolyte.

In this illustration you can see one large cell, three smaller cells and 6 very small cells and compared to the one cell battery pictured here on the far left. Important is to understand that these three different size lead acid batteries all have something in common, each cell no matter what the size has the potential of 2.2 Volts DC (2.2 Vdc). A one cell battery the size of a piece of toast produces the same exact voltage as a cell as big as a large freezer. Each cell when fully charged will measure 2.2 to 2.4 Volts per cell (100% optimum capacity). Capacity is the major difference between all of these and electrons are the electrical volume or capacity, current is the flow of those electrons. For example one gallon of water can be also said to have droplets and these droplets are exactly the same as the electron or in a specific quantity measureable they are called watts. When someone pays an electric bill it is calculated in watts and when a specific amount of droplets of water add up to occupy a one gallon container that specific volume can also be compared to the watt in the sense it is the common smallest measured amount when paying for them in a bill.

A specific amount of electrons result in one ampere or 1 Amp. The Amp is multiplied by the battery pressure or volts (EMF electromotive force) to calculate watts. The one cell at 2.2 Vdc can power something electrical that can be operated on 2.2 Vdc. When current is drawn from the cell @ 1 Amp the watts would be 2.2 X 1 or 2.2 watts. The 3 cell battery would calculate 3 X 2.2 = 6.6 volts @ 1 Amp = 6.6 watts. The 6 cell battery would calculate 6 X 2.2 = 13.2 volts or 13.2 watts @ 1 Amp current draw. Watts are used by each second of time so to calculate total watts used the seconds are the multiple.

In all cases of these batteries the optimum 100% full charge rating are those calculations given in above text. After the 13.2 Vdc lead acid battery is used or in service when checked a good battery that has been setting around for a week or so is most likely to read 12.7 Vdc to 12.58 Vdc with absolutely nothing connected to it (no load). So in the calculations that would end up to be a 12.7 / 13.2 or reduce to approximately 3.8% loss or 96.2% of battery left. So in the electrical calculations of efficiency the state of the battery results in two factors electrolyte specific gravity and percentage of charge available. A direct relation of Voltage and current exist whereas the lack of volume will result in a reduction of force potential or electrical voltage.

In an air system the tank holds the air volume and pressure results and builds as more air is pumped into the tank. After the pump reaches the desired pressure someone has set into the controls it stops. Example is the air system where they range from 100 pounds per square inch pressure to 200 pounds air pressure measured at the air tank. The volume of air is directly proportional to the dimensional size of the air tank. The volume keeps things running and the pressure is required to begin moving the load or work effort. The battery is like the air system in the way of pressure (voltage) and capacity (Amps). The cell size in a battery or dimensional volume is exactly like the air tank sizes, larger volume bigger capacity. More capacity in an electrical storage system means that the pressure required to operate an electrical device remains at the specified value and can run the device longer than a smaller cell in dimensional volume. In the days of older technology and to modern times of todays newer batteries it is fact that the type of batteries used are of a certain weight in pounds and for example a lead acid cell that weighs 100 pounds will have 100 times the capacity of the same type of cell weighing 1 pound. So the weight is actually a type of guideline for electrical capacity in the lead acid systems.

A Caterpillar equipment battery that is 12Vdc and weighs 50 pounds has more storage potential in volume than a Caterpillar equipment 12 Vdc battery that weighs 25 pounds, the concept is comparing apples to apples. After understanding that; each electrical device has it's own operating voltages dictated by the manufacturer, that voltage need to be maintained as long as the product is expected to work properly.

Most all DC low voltage systems (2.2 Vdc to 52.8 Vdc) found in solar systems as well mobile equipment rate the nominal voltages of the device powered at a commonly used 6 volt 12 volt 24 volt or 48 volt DC lower limit. All electrical devices will operate until the voltage in the system drops to a point that the device stops working properly and develops excessive heat eventually burning out.

NOTE: In all systems electrical , pneumatic, or hydraulic as the pressure drops at one point only heat is the result ending up as the product that quit operating. No matter how much volume is contained at the point of low pressure limit no work can be accomplished in any of these systems. A DC device like a motor will run fine at it's rated voltage and as the voltage drops so does the speed of the motor shaft.