As soon as it was placed on the phone, the phone did not turn on because the battery was completely discharged. Plugging in the charger and cable, the phone turned on and showed a battery percentage of 1%. During the first charge using a fast charger, it took a long time for the battery to charge up to 20% and it got quite warm. Then it charged up to 100% with much less heat, I can say at a normal level, maybe slightly more due to the fast charger. The whole process of the first charge took about 1 hour and 15 minutes. Since then, the phone has been used five times in a row and so far the battery is working satisfactorily, charging in about 50 minutes again with a fast charger but from 20% to 100% (I always try not to let the battery drop below 20% on all iPhones because it is said that this degrades it). Also, considering that a battery needs about five charges-discharges to start working properly, I can say that even at low levels from 40% to 20%, the battery started to hold up quite well at these percentages. Overall, I am satisfied with this purchase.