I understand that 5s Li-ion should be charged at 21V (4.2*5) however the only laptop chargers I can find are 19V, 20V, and 24V. Each is relatively close to the value that should be used for 4s, 5s and 6s.
Is this what they are really?
And can I use a '20V' charger to charge 5s Li-ion?