I charges the battery of my cell phone, only when it says one line inside the battery indicator or the battery indicator flashing.

@dor123, me too.  I try to give it a full "cycle", AKA fully charged to fully discharged to fully charged again.  Sometimes that doesn't happen though like if I have to go somewhere so I unplug it half-charged and take it with me, or if I know I'll be somewhere without a working outlet for an extended time I'll top it off. 

Full discharging actually produces more wear on a Li-Ion battery than partial discharging does. It's really only NiCD that's susceptible to the memory effect.

Oh interesting! So should I not let it get that low?

It's not detrimental to the battery, but constant full discharges does slightly lower cycle life. The normal partial discharges and charges it will see in normal everyday use is about the best you can treat it.

I fired up my antique iPod Touch 2nd generarion tonight for the first time since July 2013, that's when I shut it down. It still had half a battery!! After sitting almost 2 years!   I used it to post this message.

The LiIon's are practically not influenced directly by the charge cycles (you may easily reach 10000's of them, as well as wear the battery just after barely 10 cycles and it will still be a normal LiIon wear - the life just depend on other conditions than charge cycling).
The problem is, people are not aware about these effects at all and very frequently treat their batteries wrongly.

For the LiIon there are two cases limiting the life:
1) Time spent in charged state, accelerated with temperature. So if you charge the battery to it's maximum and leave it there behind the car window in the summer, after few days the battery is dead.
Sanyo recommended for a float charge systems (keep the battery "fully" charged all the time) to use just 3.9V top charge limit. That means capacity reduction of about 20%, but life increase by factor of at least 10 compare to standard 4.2V specification.
And of course, keep the cells away from any heat source - 10degC temperature increase means half of the life...
The thing is, the standard battery endurance tests just let the cells cycled (fast charge, fast discharge,...) and evaluate the performance loss as a function of number of cycles. That pretty well matched the degradation mechanisms with NiCd and NiMH, but it is completely useless with LiIon's. It leads to figures like 50k+ cycle endurance or so. With not really serious makers you may read these figures as the rated endurance, but for a real everyday use that is nonsense, because mainly the time dependent degradation kills the battery way earlier.

2) Someone states underdischarge (below ~2.5V across the cell), it will kill the internal chemistry. However I haven't found any detailed literature explaining that, except the possibility for the charger electronic to distinguish that from a damaged cell, so chargers tend to refuse charging cell with such low voltage (it is a fire protection measure, as charging attempt on a damaged cell could be very dangerous)
So I would guess this is rather a consequence of that fire safety measure than a real problem of a good cell.

My Samsung had OK battery life, but I'd plug it in overnight.  If I couldn't plug it in, it would last 2 days but would be in the red by bed time the second day.  For some reason though, occasionally it would decide to have a "turbo discharge day" and for whatever reason would be dead by lunch time, despite being plugged in the previous night.  I haven't tested the endurance of the iPhone beyond 2 days, but after 2 days of use, it's not demanding a charger like my Samsung would.  In reality though, it spends a fair amount of time each evening tethered to my computer or plugged into the car stereo, which keeps the battery pretty well topped off.  With that, I don't do the overnight charging most nights.

Just disable the automatic updates and run the updates only when connected to the charger.
Or at least enable the updates just via your home WiFi. The experience is, the updates run regardless of the battery state, nor phone temperature. My co-worker removed the phone (he had it 3'rd day or so) from it's bag and it was severely hot. After looking on it in more detail, he have found the update via the cell phone network was in progress. The only reason for the high temperature was just the power dissipation from the processor activity for the running update. Disabling all updates except the home network and it never happened again...

Sadly it's not the only cause for excessive battery drain(at least on android). Sometimes apps that use wakelocks( a system to allow apps to run periodically in backround like a service) hang and keep consuming cpu cycles until the battery die. The updates normally take only a few minutes so they drain only a few % of the battery.

BTW I have Samsung galaxy S2

I think that was it.  I had it set to only update on Wi-Fi, which was generally kept off.

The updates normally take only a few minutes so they drain only a few % of the battery.

If it is some more major update, like the first one after purchase (that was the case I have described), it uses to take quite long, mainly on slower network like the older GSM data service systems.
Draining the battery was not the most severe problem of such unexpected activity, but it was the heat it generated. Because it was not expected, he had the phone inside a pouch in a bag pocket, so everything but decent cooling...

I use a Samsung S4 which I got in June 2013, but ever since around October 2013 a some sort of glitch with the WIFI option was playing havoc!! (When I press the WIFI button on, it stays dark green for a while then returns to Grey meaning OFF- my WIFI won't turn on!)

My first smartphone was the Samsung Galaxy S which I got back in March 2011 (nearly 4 years ago!- time flies    ) and it was a very good smartphone. But in early 2012 the Android App Market (old name of Google Play)  expressed the Error 101 meaning that I could not download apps, but it wasn't too much of a probs as its WIFI and features like Gmail and text messaging kept me happy- especially when I was writing emails to my friends when I was on the USA holiday in summer 2012! Text messaging was too expensive whilst in USA roaming mode so therefore had to use Gmail via WIFI

Now going vintage, I've got a LG KT520 which I got for my 12th Birthday back in 2008  looked very exciting at the time as I've used it as a mini camera with 3MP camera, but as I saw the Samsung GS phone, I wanted it!

But also in the early months of 2008 (Winter/spring) my mum and dad got themselves two Nokia 2310 phones which had the red theme colour  surprisingly its now rare in this day?

Flurofan96 

Here are my phones...
- 2002 Nokia 5165 (recycled)
- 2003 Nokia 6360 (recycled)
- 2005 Nokia 3560
- 2006 Sony Ericsson Z500a (recycled)
- 2007 Sony Ericsson W200a
- 2008 Sony Ericsson W580i
- 2008 Motorola W376G
- 2009 Sony Ericsson Z750a
- 2010 Samsung A767 Propel (recycled)
- 2012 Samsung Rugby Smart
- 2014 Apple iPhone 6

The 5165 was my first phone.  Though obsolete, I kind of wish I had kept it because it was still in working condition.  The 6360 was my favorite of my early Nokia phones, but it died in an unfortunate work accident and was recycled.  The 3560 was a replacement my work bought me, and was my last analog/digital TDMA phone.  Had a color screen and polyphonic ringtones, though none of the built-in ones were good.  The Z500a was my first GSM phone.  One day I had lost it, and someone later found it in a mud puddle.  Due to the wallpaper I had on it, it made it's way back to me, but the water had gotten into the display and it later failed.  I got the W200a to replace my display-less Z500  It was my smallest phone, and first in a series that could take M2 (micro-memory stick) cards.  I got the W580i when my carrier was acquired by at&t and I migrated over to them.  Unfortunately it had some bugs, and when I attempted to preform a software update, it failed and bricked.  The Z376G was a cheap prepaid phone I got while I was working in Louisiana, and needed a local number.  The Z750a was the replacement for the failed W580i, and was my favorite of the flip/bar/slider phones that I had.  After 2 hard years, it was starting to develop crashing issues.  I kept it as a backup.  My dad had a refurbished Propel on hand, and gave it to me.  It was a QWERTY slider phone.  It died when I forgot to take it off before doing rescue drills in the river.  The Rugby was my first smart phone.  It was a "rugged" smart phone, and with my history with phones, seemed like a good idea.  It was solid on the outside, but was limited inside by its single core CPU and only 512MB of RAM.  Did the job, but it was sluggish.  The iPhone 6 in the otter box is my current phone.

I just got a Samsung Galaxy S4 (AT&T SGH-i337) (Even with the contract the S5 was too expensive for me) to replace a Samsung Galaxy Mega (AT&T SGH-i527) that I was unhappy with
I have a two year contract though as unsubsidized phones are very expensive 
I am happy with the S4 I just wish I could get rid of all of the junk pre-installed android apps that I can't seem to get rid of as it will not let me but I guess that is the price I have to pay for getting a contract phone