22 Years' Battery Customization
Jun 11, 2020 Pageview：3724
The capacity of any battery can be measured in either watt-hours(wh) or milliamp-hours(mAh). The choice of the two normally depends on what the battery manufacturer chooses to use and in some cases the battery capacity itself. A couple of times you will notice that capacities of batteries with larger capacities are normally specified in watt-hours and those with smaller capacities in milliamp-hours.
One may ask why it’s important to calculate the battery capacity in watt-hours if you already know its capacity in milliamp-hours. One of the reasons for converting mAh to wh is because there are some situations when the battery capacity requirements are specified in wh and you will need to convert the mAh to wh to know whether your battery meets such requirements.
For instance, a plane company may specify the maximum battery capacity required on board in wh. So, you will have to convert your battery capacity to wh in order to know whether it qualifies to be on board or not. There are several other cases where the battery capacity requirements might be specified in watt-hours and you would to have to convert your batteries capacity to wh to know if you meet such requirements.
How do you calculate battery Wh?
The watt-hours(wh) of a battery can be calculated using two methods.
Method 1: Using nominal voltage a maximum current
In most cases the voltage rating of the battery is fixed and it entirely depends on its internal chemistry. For instance, the voltage of Li-ion battery will be different from that of a NiCad battery. On the other hand, the current of the battery depends on how much the target device is able to draw at a time.
However, batteries have a limit of the maximum current that can be drawn from them. In this case, the maximum current is what we are going to use to calculate the watt-hours of battery. To calculate watt-hours, you will have to multiply the voltage of the battery by the maximum current and then the time in hours. (watt-hours) = Voltage(V)*Current(A)*Time(hours).
This equation simply shows the maximum amount of energy a battery will be able to supply in an hour. Which is the real essence of the wh units. If we consider a Li-ion battery with a nominal voltage of 3.7V, a maximum current of 5A. The watt-hour rating of such a battery would be calculated as follows;
watt-hours = voltage*current*1hour= 3.7*5*1(wh)=18.5wh. This means the maximum energy this battery can provide in one hour is 18.5wh.
Method 2: Using milliamp-hour rating and voltage
The second method for calculating watt hours is when you are given the milliamp-hour rating of the battery and its nominal voltage. In a couple of situations, the battery capacity will be given in mAh or Ah. If you need to the equivalent wh rating when given the capacity in mAh, you will need to know its nominal voltage as well. With the nominal voltage and the mAh rating, you will be able to calculate the equivalent Wh rating as follows;
Watt-hour(wh) = Voltage(V) x milliamp-hours(mAh)/1000. If you don’t divide by 1000, you will have calculated the watt-hour rating in milliwatt-hours instead of watt-hours. Let’s consider an example of a battery with 3000mah and a nominal voltage of 3.7V. Its wh rating can be calculated as follows;
Watt-hours(wh) =Voltage(V)*milliamp-hours(mAh)/1000 = 3.7*3000/1000=11.1wh. So, a battery with 3000mAh and 3.7V nominal voltage will have a watt-hour rating of 11.1wh.
Watt-hour(wh) calculator
A watt-hour calculator is based on any or both methods we have shared above. So, its algorithm has to be written to accept either voltage and current as the inputs or voltage and mAh rating. So whenever, one wants to calculate the wh rating of the battery, they simply punch in any of the two sets of inputs and the calculator will compute the equivalent value in watt-hours(wh)
What does WH mean on a battery?
A watt-hour(wh) basically means the amount of energy the battery is able to give within one hour before draining. It can also be looked at as the maximum power a battery can supply in one hour before draining out. This means if the power requirements increase, the battery will be drained in less than an hour.
For example, if a battery has a watt-hour rating of 60wh. This means such a battery will give 60watts in one hours before it drains out. Incase the device using such a battery draws less than 60W (which is normally the case), the battery will last longer than one hour. If say the device draws 30watts, then the battery will be able to power this device at full capacity for two hours.
On the other hand, if the device is drawing 90W, then the battery will be drained in 40 minutes. That’s the simple interpretation you should get whenever you see the watt-hour rating on a battery. This means a battery with more watt-hours has the capacity of lasting longer than one with less watt-hours if connected to the same device.
How do you use a battery WH calculator properly?
To use the WH calculator properly you need to be having the correct inputs. From the two calculations methods we saw above, to calculate the wh rating of a battery, you will need to know either voltage and current or the mAh rating and the nominal voltage of the battery. If any of those parameters is missing, then the calculator won’t have enough data to do the calculation
Like we have seen above, for most batteries the nominal voltage is always the same for all battery capacities, it is the current and the mAh rating that may vary. For example, most Li-ion batteries have a nominal voltage of 3.7v. For some batteries like those used in laptops, several Li-ion or Li-PO cells are connected together in sets of 3 cells which may increase the nominal voltage to 11.1V. Most of the smartphone batteries will always have a nominal voltage of 3.7V.
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