IPad mini must be plugged in to turn on even if battery is fully charged

Deeper discharge/charge cycles shorten an Li-Ion battery's lifespan faster that shallow ones. (e.g. One 100% cycle is more wearing that four 25% cycles, etc.) Therefore, keeping an iPad or iPhone on a charger or always topped off between short uses will tend to lengthen the battery's total lifespan by reducing the number of deeper cycles per annum, all other thing being equal (such as total time of use).

"Calibrating" has almost nothing to do with the battery lifespan. It's mostly needed to help the battery gauge icon behave more accurately. Once or twice a year is probably good enough for that purpose.

I can not repair your battery, but try to provide you with information to decide if the battery is EOL.

There are 3 conditions reported.

Replace Soon: The battery is functioning normally but holds less charge than it did when it was new.

Replace Now: The battery is functioning normally but holds significantly less charge than it did when it was new. You can continue to use the battery until you replace it without harming your computer.

Service Battery: The battery isn’t functioning normally, and you may or may not notice a change in its behavior or the amount of charge it holds. Take your computer in for service. You can continue to use your battery before it’s checked without harming your computer.

In About This Mac-- more info look for battery information such as:

Charge Information:

• Charge Remaining (mAh): 2147 (it shows this at 40% remaining based on current consumption)

• Fully Charged: No

• Charging: No

• Full Charge Capacity (mAh): 4829 (this indicates the age, or the capacity of the Battery)---> on a new and healthy battery for my MBA that should be in the range of 7500 mAh, so I lost some over 2 Years of use.

Health Information:

• Cycle Count: 480 (this is my battery on MBA 2012)

• Condition: Service Battery :(

• Battery Installed: Yes

• Amperage (mA): -1458 (this is your current consumption)
• Voltage (mV): 7612 (this is also a indicator of your battery health in how well can it keep the Voltage at load)

There is a circuit mounted on/in the battery, not part of your computer but part of battery, that reports battery information to your computer. That information is then used to present you with the battery conditions. If that circuit is faulty, you have to replace the battery, even if the battery it self is still in a good condition. There is no way to reset or repair that circuit.