I built a power bank which had Seven 18650, savage some from laptop batteries and others from an old power bank... I recently just noticed that the power bank circuit won't charge the batteries though the output process is good to go... It came to my knowledge that charging the batteries directly from the charger would severely damaged the batteries.. So I dropped the voltage using two diodes connected in series, it gave me 4.0V, I don't need an ammeter to know that the diodes also took down the current, because it took an hour and half to charge a 18650 from 2.8V to 3.2V meanwhile I'm using a 5V 1A charger... So any help on how to increase the current or any alternative to charge a 3.7V 18650 using a 5V 1A charger. Thank you in advance for your anticipation on getting me a solution.. Forgive my English, its crappy.
ATTENTION! If you overcharge a lithium-ion cell it can explode and cause some serious damage. Also if you get the cell into undervoltage condition and try to charge it again it will explode too.
This is why lithium cells should never be used without a battery management system which supervises every cell condition.
Lithium cell should be charged with a CC-CV algorithm. Every cell is different about the end of charge voltage, under voltage border, maximum currents and so on. Without out knowing anything about the cell I would not risk burning down my house while experimenting with lithium-ion cells.
Mixing different cell types can also be dangerous because there can be compensations currents which are not intended.
(Source: I work at a company which develops battery management systems and builds battery packs. Even with a high experience we have burning cells from time to time for example when we get packs back from a customer and do not know what he has done with it.)
Designing battery charging system is a complex task with lot of precautions and calculations. That's the reason many battery management ICs are available in the market. The general features of such ICs are Charging type CC, CV or trickle charge mode, battery deep discharge protection, battery over charging protection, temperature monitoring while charging, etc.
These are the essential parameters which needs to be considered for designing battery charging circuit and any of these parameters going out of range may result in the explosion in the battery.
So, battery way is to search for good full featured Battery management IC and understand each of its parameters and their significance. Then you will be able to design a proper battery charging system for your power bank.
Also just by increasing the charging current by few hundred miliamperes will not give you desired results of fast charging. There is a certain limit of charging current depending on battery capacity, which needs to be follow in order to keep your battery healthy.