when should i plug in the charger immediately?

[preppystud]

it gives warning to charge it around 20%. but when is it urgent to charge it immediately before the battery is damaged?

 

[Aquila]

With the 2013 it's not really ever urgent, but it is a better idea to not let it actually power itself down due to loss of charge. So, I guess prior to 1%. The 2012 version had (has) an issue where it can be in a lot of trouble if it runs out of juice (some of them are difficult to power back on and some don't come back), but that seems to be a non-issue on the 2013. That said, like always it is better to have it topped off than low - but better doesn't make it urgent.

 

[gerryp123]

I've had mine down to 5% with no problem.

 

[jerrykur]

It will probably power off before it gets too low. But if it did power off I would not leave it uncharged for too long since the battery will still be self-discharging.