Why do newly bought phones have to be charged for seven to eight hours at a stretch?

Nowadays, smartphones come with lithium ion (Li-ion) batteries with partial charge that can get fully charged within about 2 h.

However, manufacturers still insist on charging them for 8 hours before the first use. This is probably because the charge levels indicated when a new gadget is first switched on, may not indicate the true level of charge in the battery. If the actual charge is very low, when you switch on the new phone and start installing apps it may get switched off in between. The manufacturer does not want the customer to have a bad first impression!

 This instruction has its origin when nickel-cadmium (Ni-Cd) batteries, containing nickel oxyhydroxide (NiOOH) as positive electrode and cadmium as negative electrode, were used. These batteries are known to have a memory effect. In other words, the battery seems to memorise the discharge voltage and the depth of discharge of the previous cycling. This effect leads to the progressive loss of practical cell capacity at a fixed cutoff voltage and hence leads to large wrong estimation of the state of charge of the cell

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