Why is my ipad being charged at low speed and sometimes discharged even when plugged in? When I plug in my tablet and use it normally at normal brightness or even not using at all, its battery is often discharging (at 20-2000mA)



and when it charges the speed is very low (only 300-500mA)



The tablet also runs undervoltaged and shuts down at 30% battery discharged and at 15% plugged in. Can you tell me how to fix?
If you charge from a standard USB port (on a PC) or an ordinary USB charger, it is quite normal to charge with up to 500 mA. This is the maximum you can get.

If you want to go beyond that, you'll need a USB 3.0 port or high speed chargers. For example Apple supplies special 10W, 12W, 18W etc. chargers for various iPads.

It is also normal that an iPad is capable of consuming more power than a 500 mA charger supplies. Therefore you can experience that the iPad is discharging the battery even when it is connected to a charger.

To avoid that, close power hungry apps (i.e. don't be playing an intensive 3D game while looking at your battery stats for example), and/or use a higher capacity charger.