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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)

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

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The tablet also runs undervoltaged and shuts down at 30% battery discharged and at 15% plugged in. Can you tell me how to fix?

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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.

  • While the usb 2.0 spec only allows for 500mA, many computers now supply 900mA to 2300mA over usb ports. Apple laptops in particular will provide 5-12w through their usb ports. The usb 3.0 spec is 900mA. I've observed a 2008 macbook providing 1200mA to an iPhone. – Jared Menard Jul 25 '18 at 14:14
  • Yes, I know - I’m just explaining that it is not an indication of anything being wrong if you see 500 mA charge. Of course you can get much more with various chargers and modern computers. – jksoegaard Jul 25 '18 at 16:09
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If you tablet is charging slowly, then your power supply is probably under-powered. Make sure that your charger brick is at least 5v and 1Amp (5w). If possible, use the charging brick that came with your tablet.

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