PowerBanks have two key ratings:
- the maximum power that it can output to charge a connected device (measured in Watts - W). This value matters as it determines whether or not the PowerBank can output adequate power to charge a device.
- the PowerBank's total power storage capacity, usually measured in MilliAmp Hours (mAh) - or Watt Hours (Wh). This value determines how much power is stored by the PowerBank's own battery when itself is fully charged.
To cite an analogy... think of a water tank and the hose connected to its outlet. In this analogy the water tank is the PowerBank's own battery, the size of the hose equates to the power output of the PowerBank - and buckets that are filled from the hose are the devices that you intend to charge.
The total capacity of the water tank determines how many buckets can be filled from the tank when it is full. You can obviously fill fewer large buckets than smaller buckets - and by extension, if a bucket is larger than the tank, you can't completely fill the bucket.
As such, the tank needs to be sufficiently large (mAh) for the buckets that you intend to fill.
Now for the hose - the size of the hosepipe (power output of the PowerBank - W) determines how much water can flow through the pipe in a given time; larger hosepipes can empty the tank faster than smaller hosepipes. The hosepipe needs to have adequate flow for whatever is connected to it - such as a garden sprinkler. If the flow to the sprinkler is insufficient, you might only see a dribble through the spray-head, or nothing at all.
An iPad typically requires a charging supply of at least 12W; any less and charging will be very slow, or the iPad may not charge at all. Most iPhones can charge, albeit slowly, from power sources rated as low as 5W.
PowerBanks with a low capacity, such as those intended to charge an iPhone (that has a much smaller battery than iPad), may only have adequate capacity to partially charge the iPad's battery.
Hopefully you now understand the relationship between the total capacity of the PowerBank and its maximum power output - and therefore can now gauge the potential suitability for the device that you intend to charge.
In summary, the PowerBank battery must be much larger, with a greater power output, to successfully charge an iPad - than would otherwise be the case for an iPhone or other small rechargeable device. A greater PowerBank capacity allows you to recharge more or larger devices. 🙂
Assuming that your PowerBank has both adequate capacity and power output, you may also need to consider the type of USB connection...
If the PowerBank (or Power Adapter) has a USB-C connection, it must support USB PD (Power Delivery). Apple devices do not support other proprietary charging standards such as QC (Quick Charge). Recent iPad models can charge at 20W or greater when charged from a USB PD power source.
If the PowerBank has an older USB Type-A connector, it must be able to output at least 12W. When charged from a USB Type-A power source, the iPad will typically limit its charging rate to 12W (i.e., 2.4A @5V).
