I have Lenovo 720s, the original adapter is 20v 3.25a (65w), it's also written on the bottom of the laptop.
I'm planning to buy an external battery to charge my laptop, I found one with output up to 19v 3.5a (66.5w), can I use that external battery to charge my laptop? Is it harmful to my laptop or the external battery? Will I be able to charge my laptop with full speed if I use that external battery?
I also found one with 20v, but only 2.25a (45w), will it be a better option to pick this one instead?