All this info is around many times but I wish one of the experts in electric power would write a pushpin article that answers the following battery questions.  That way it will stay at the top of the forum for new comers to read.

1. Define the common Lipo terms.  2S, 3S, 4S etc. 20C, 30C etc.
2. Fully charged what is the voltage of a Lipo cell.
3. Can Lipo cells be run in series and parallel.
4. As a rule of thump what is the fastest charge rate for a Lipo pack.
5. What is the lowest safe discharge voltage of a Lipo cell
6. What is the proper way to store Lipo cells - long term, short term
7. How real is the fire / explosion dangers of Lipo cells. What is a safe setup to charge Lipo packs unattended.

I know the answers to most of these questions (or at least I think I do) but they seem to keep cumming up.

                          

John
I’m no expert but I will try to answer the 7 questions.  Looks like Igor and I worked on it at the same time and my answers may be redundant but I will post them anyway.
1.  Define the common Lipo terms.  2S, 3S, 4S etc. 20C, 30C etc.
2S, 3S refers to how many cells are wired in series.  “S” refers to series - so a 2S means 2 cells are wired in series 3S means 3 cells in series.  The result is the voltage is an “S” multiple of cell voltage (nominal 3.7 vDC Lipo batteries cell voltage times “S” or 7.4 volts for 2S and 3S equals 11.1 volts.    Mille Amp Hour (mah) rating would remain the same as labeled (see question 3).  20C, 30C is a rating that the manufactures place on their batteries to reflect the discharge capability of their batteries.  So, on a 20C rated battery you could discharge an 1800 mah capacity battery at 36 amperes.  On a 30C 1800 mah rated battery, the maximum discharge rate could be 54 amperes.  Note: On some low end batteries this rating is unreliable and caution should be used in discharging at the full rates.  
2.  Fully charged what is the voltage of a Lipo cell?  Standard Lipo batteries are charged to 4.2 vDC per cell.  So if you run a 5S pack, meaning 5 cells in series, the fully charged pack is 21 vDC although the nominal rating is 18.5 vDC.  5 X 3.7 equaling 18.5 vDC and a fully charged pack is 5 X 4.2 equaling 21 vDC.
3.  Can Lipo cells be run in series and parallel?  Yes, they are run in Series most of the time but the Pattern Fliers run Parallel packs often to gain capacity.  Note that the packs are run in parallel but disconnected and charged individually.  If you have two 4S packs with 1800 mah capacity and you wanted to maintain the 14.8 vDC nominal voltage but increase duration you could construct a connector that allowed the two packs to be plugged into the ESC in parallel. The capacity would then be 3600 mah.  Safety hint DO NOT try to charge these in parallel you will screw up the balance of the cells.
4.  As a rule of thumb what is the fastest charge rate for a Lipo pack?   The short answer is 1C which means 1 times the rated mah rate of the battery pack. Example if you have a 5S 1800 battery pack then you can charge it at 1800 ma or 1.8 amperes (a) be sure to set the charger to the correct number of cells (5 in this case) and then set charge current to 1.8 a.  Some high performance battery cells allow higher charge rates, ThunderPower just came out with cells rated at 12C charge rates and discharge rates at 65C.  Meaning that an 1800 mah battery can be charged at 21.6 Amperes and the battery can be discharged at 117 amperes. Wow!
5.  What is the lowest safe discharge voltage of a Lipo cell?   Standard Lipo batteries 3.0 vDC per cell.  So 3.0 vDC X numbers of cells or on a 5S 1800 battery 3 x 5 or 15 vDC. Many folks set the low voltage cutoff on their ESC to 3.2 vDC per cell - this is conservative but I think prudent.  
6.  What is the proper way to store Lipo cells - long term, short term?  Short term meaning from flying session to flying session (less than a month, normally weeks). I store mine charged and ready to go from week to week. Long term meaning over the winter store at 3.8 to 3.9 vDC per cell.  Check voltage with voltmeter and maintain the charge at 3.8-3.9 vDC for the duration of storage time.
7. How real are the fire/explosion dangers of Lipo cells? What is a safe setup to charge Lipo packs unattended?   Always think safety.  Last question first – don’t leave your batteries to charge unattended.  Many batteries have gone up in flames, 99% of the time it is operator error.  The most often cause is the wrong kind of charger or wrong settings programmed by the operator.  Here are some common sense things to think about maybe they will save your car or house from going up with your batteries.
  a.  Get a reliable charger that is purpose built for the job of charging Lipo batteries.  Lear how to use the charger properly. I know 99% of the folks reading this are male and “we don’t need no stink ‘in instructions” but for once read the instruction.
  b.  Get a Lipo charge bag or fireproof container to place your batteries into during charging.
  c.  To transport your batteries follow Paul Walker’s lead and get a fireproof “Safety Box” from Lowes or Home Depot.  They are about $25 from Lowe’s.
  d.  Check for bad connections on all parts of your electrical system often.  

John
I will edit my above post some and ask Dean to post in the pushpin section.  Good questions.

Norm

Hi John,

All the answers you received are right on the money, and if you want to go one step further, I've written an article on keeping statistics when charging Lipo batteries.   It appears in the current issue of Stunt News on page 58 and 59.
I hope you find it interesting and helpful.

Ron Heckler
New York Control Line Stunt Team

Guys
The battery questions are posted on   ....fesselflug.eu/html/battery_questions_answered.html
Igor and I jointly combined our answers - hope it helps some of the new and old guys.

Norm

Right ... you must know type of balance connector on the battery and your charger must have the same. Fortunately you need only dedicated balancer cable between charger and the battery.

Ward,

Seeing is easier than explaining.  Lipo batteries we use, have at least two different type of  plugs for the balance connector.  Thunder Power uses one and most of the Chinese batteries use the other.
Some chargers come with more than one type, others you have to buy another adaptor.  They're not expensive.  It's best to balance the battery when charging.  Balancer goes between the battery and the charger.

Hey! I think I'm getting this...

In order to charge a battery you need:

     1. A battery
     2. balancer/connector that matches both battery and Charger
     3. a charger
     4. And maybe, an AC/DC converter

Now, am I to ASSUME (I hate that word!) that all batteries (of equal voltages) and chargers perform alike, and you just need the correct balancer/connector?

That's gotta be too easy... 

W.

I am not quite up to date on the latest chargers.
Mine needs me to set correct voltage or number of cells and the maximum current I want to allow. It is also happiest when fed from a ... 12V battery!

But that's ancient technology from about 5 or 8 years back...

Your old one Sounds like a peak charger for Ni Cad packs.  DO NOT USE ON Li Po packs.  A cheep Li Po charger that seems to work is the B6 Li-Po RC Battery Charger BK found on eBay.  Just search for "B6 Li-Po" and a bunch at different prices will pop up.  It will charge all types of batteries.   It is only somewhat user friendly so setup can be a little tricky.  However if used correctly it appears To do it all.

You want a balancing charger ... preferrably one with the balancer built-in, not an add-on.
I will stop short of suggesting brands but excellent stuff can be had for $50 or $60 and domestically made too!
Dean P.