1 - whatever they say in the manual
2 - if you'll be needing to use the device for a long period of time without the ability to recharge it, then charge it up to 100%
3 - otherwise, topping it up to 80% when it reaches 20% is a reasonable thing to do
1 - whatever they say in the manual
2 - if you'll be needing to use the device for a long period of time without the ability to recharge it, then charge it up to 100%
3 - otherwise, topping it up to 80% when it reaches 20% is a reasonable thing to do