If a lithium-ion battery must be left in the charger for operational readiness, some chargers apply a brief topping charge to compensate for the small self-discharge the battery and its protective circuit consume. The charger may kick in when the open-circuit voltage drops to 4.05V/cell and turn off again at a high 4.20V/cell. Chargers made for operational readiness, or standby mode, often let the battery voltage drop to 4.00V/cell and recharge to only 4.05V/cell instead of the full 4.20V/cell. This reduces voltage-related stress and prolongs battery life.
Some portable devices sit in a charge cradle in the on position. The current drawn through the device is called the
parasitic load and can distort the charge cycle. Battery manufacturers advise against parasitic load while charging because it induces mini-cycles, but this cannot always be avoided; a laptop connected to the AC main is such a case. The battery is being charged to 4.20V/cell and then discharged by the device. The stress level on the battery is high because the cycles occur at the 4.20V/cell threshold.
A portable device must be turned off during charge. This allows the battery to reach the set threshold voltage unhindered, and enables terminating charge on low current. A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low. A battery may be fully charged, but the prevailing conditions prompt a continued charge. This causes undue battery stress and compromises safety.
Battery professionals agree that charging lithium-ion batteries is simpler and more straightforward than nickel-based systems. Besides meeting the voltage tolerances, the charge circuits are relatively simple. Limiting voltage and observing low current in triggering "ready" is easier than analyzing complex signatures that may change with age. Charge currents with Li-ion are less critical and can vary widely. Any charge will do, including energy from a renewable resource such as a solar panel or wind turbine. Charge absorption is very high and with a low and intermittent charge, charging simply takes a little longer without negatively affecting the battery. The absence of trickle charge further helps simplify the charger.
I have read this on batteryuniversity.com what does it exactly say and is it correct?
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charging your phone correctly
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My first words were about outdated gear. All the phones at the office are fine with ABC. But there are some folk that want to dive into discussions about battery minutia. I'm not going to do that here.
Batteries have about 300 cycles of great life and the tricks to extend that are rarely employed because folk want the run time. You can fault that but I will not duplicate prior discussions.
Why?
"It's a trap."
Bob
It says you should turn off your phone while charging. Is that true? Why?
If the maker tells you to do that, why not?
There are thousands of discussions about phones and batteries. Since I want my phone ready to go and I get years using ABC, I'm made my choice.
Can you make yours?
Bob
Why not?
Because to do ABC I will have to charge my phone throughout the day. And I will turn it off everytime? How will I receive calls?
I'd consider a replacement as of the dozen phones at the office, all are using ABC and many others before that. Remember it's a trap to discuss battery minutia but in your case, it's clearly defective and not meeting your needs.
Bob
Sorry, my native language is not english. Can you write post in an easier English for me please 
First of all, stop reading everything so literally. I read/write/speak other languages besides English too, and have figured out that this usually gets me in a heap of trouble 
Anyway, yes- it's fine to leave you phone 'on' to receive calls during the day, but plugged in and charging (hence, ABC). At night when you don't typically get calls, then keep charging but turn it 'off'.
Enjoy your phone!
For getting the most out of your phone's battery, never let it go down to complete 0, that is when the phone goes off automatically instead of activating power saving.
Try keeping the charge from 25-85% at all times, and of course 100% when possible( if you have wireless charging, it will help do the job ).
+If you have the option to ''Trickle charge" your phone when nearing 100%, that is the best thing.
Enjoy your phone even more! 
All the charging potential problems go away for me when I buy products with replaceable batteries. So I have a Samsung Galaxy S3 with a cheap replaceable battery. It was the very top priority for me when buying a smartphone.
I also have a Sony VAIO Flip 14 laptop for which Sony posted a video on youtube showing how easy it is to replace the battery at it's end-of-life.
I'm very disturbed by all of the products on the market with non-user replaceable batteries and will stay away from them as much as I can.
For simplicity I charge my Samsung Galaxy S3 all night every night and don't worry if I'm damaging the battery. So far so good.
The only thing you need to worry about is what is correct for YOUR phone and its battery. Check your instruction booklet, READ DIRECTIONS and follow them. It's that simple.
If you don't have your instruction book then get on line and download it from the manufacturer's site. If you still don't understand what to do about correctly charging your phone battery then call your phone service carrier and have them explain it to you.
Some, even most, carriers send out updates to the phones software for their systems at certain times of the night so you want to find out when that is so that you don't miss out on these updates. Missing them can cause undesired problems ranging from barely noticeable to downright malfunctions requiring extra time spent having them do it manually for you which can be a bit of a PITA. (Pain In The Ass).
Personally, I have a four year old Samsung Rugby II and, when I can, I try to allow it to shut itself off before charging. This doesn't always happen, but it happens enough to keep the battery from getting a memory (Why take chances, eh?). When I can't allow the phone to shut itself off I wait until it only has one bar in the batter meter or the battery meter is flashing to shut it off and charge it over night. I do not have internet capability on this phone turned on so I don't use the battery for anything but calls and the tiny bit of texting that I do at times. I have not had to replace the battery, yet, since I bought the phone in September of 2010.
There is no such thing as 'battery memory' on newer Lithium ion batteries. That's serious old school, amigo. Even prior to your Rugby, FWIW. A little more research on your end is required(!)
In reality, most of the current crop of Lithium ion batteries used by our smartphones could be charged/managed quite similarly since the tech is the same. 'ABC' still applies.
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