Wow. After reading a few of these last pages, I just realized how little people know about battery.
There are too much generalization about lithium batteries these days and I hope to clear up some misconceptions.
The term "lithium ion" is actually a general term for many different chemistries of batteries. It's like calling an Asian person "Chinese" or a Hispanic, a "Mexican". To the common layperson, this may be acceptable but allow me to clarify and introduce some of you guys into the culture of batteries.
Currently, the best commercially available batteries are made by a company called A123 Systems. They make their world famous Lithium Nano Phosphate batteries that can be discharged in EXCESS of 90C. For those of you not familiar with C rating, read below. In fact, I'm going to list the basics and explain it so you guys can understand it the way I do.
Voltage. Voltage is electrical pressure. The higher the voltage, the more potential power a battery has.
Amperes or amps. Amps is electrical flow. Think of amps as a hole at the bottom of a dam. If there were 2 hole of the same size in a dam and one of them is at the top while the other is at the bottom, the hole at the bottom will "flow" more water (electricity) because there is more "pressure" at the bottom of the dam.
AH or Amp Hour is the measure of how many amps a battery can discharge or "burn through" in 1 hour. For example, if a battery has 20 AH, it can discharge at 20 amps continuously for 1 hour. This also means it can discharge at 1 amp continuously for 20 hours. Get it?
To put it in clearer perspective, our battery is 1440 mAh or 1.44 AH. This means that it can discharge 1.44 amps continuously for 1 hour before it dies.
There are a few lithium battery chemistries available on the market today and it's important to know and understand them.
Lithium Nano Phosphates are the Bugatti Veyron's of batteries. For those who don't know cars, the batteries on our phones are like Corollas whereas the best of the best are Skylines, Ferarri's, etc and so on.
The order from my knowledge goes.
- Lithium Nano Phosphate (A123 Cells)
- Lithium Manganese (Sony Konion Cells)
- LiFePO4 (Lithium Iron Phosphate)
- Lithium Polymer
- NIMH
- NICD
- SLA (Sealed Lead Acid)
The chemistry in our Samsung batteries are
probably an upgraded cell of Lithium Polymer. This is from my educated guess and I will explain why. A123 cells are made in America, Konion Cells are made in Japan and everything below that are outsourced in China. Looking at the Samsung Moment's battery, it says "Made In China Finished in Korea". This Confirms to me that these are Lithium Polymer cells.
Using the process of elimination, they cannot be 1 and 2. 1 is made in the US and 2 is made in Japan. This battery cannot be a Lithum Iron Phosphate because LiFePO4 batteries require each cell to be very close in voltage and capacity and this can only be done effectively with an onboard BMS or Battery Management System.
Okay, I am straying far off topic. Getting back to the text I previously bolded, I want to kill a misconception about Lithiums. Lithium batteries in general have very high C rating. a C rating is proportionate to the AH of a battery. For instance if a battery was rated at "1C" and it had 1AH, this means that it can max discharge at 1 amps. If the battery had 2AH and 1C rating, it can max discharge at 2 amps. To put it in comparison between the top battery chemistries, and the chemistry that is in our cell phones. think about this.
A123 cells can charge and discharge at about 90C max. Our generic lithium poly can safely be charged and discharged at 1C max. Does this sound dangerous? This brings me to the common misconception about exploding batteries and today.
When a Lith-ion battery "explodes" it gets short circuited and discharges all of it energy rapidly creating lots of heat. Manufacturers sometimes cut costs and employ "cheap" Chinese battery manufacturers that build the old style cells. New cell construction have holes that open and vent gas when the battery fails preventing an explosion. Unfortunately, when we hear about exploding laptop batteries, we connect the stigma with the batteries itself when we should blame the manufacturer.
The "fuel" in our batteries are measure in
Watt hour. Watt hour is Voltage X Amps. Our Samsung Moment battery is rated at 3.7 Volts and 1.44 AH. This means it has the total energy of 5.328 watt hour. (Un)fortunately Li-poly chemistry as well as most Lith-ion with the exception of Lithium Manganese, have very high discharge curve. This is a good and a bad thing. This means that the voltage stays very high up until the battery dies. When the battery dies, voltage drops dramatically. With normal use, voltage will remain high while drawing small amps. Under cpu intensive work or hard use, voltage sags a bit with our batteries. This is very important.
My guess is that our battery monitors (programs, widgets, etc) do their best to calculate the batteries WH and it keeps tract of this partially through voltage readings. Because lithium-polys have a high voltage curve before dying, the measurements and readings are very much dependant on the voltage level. Under heavy load, voltage may sag a bit even if you have plenty of life left.
For instance, I am using the widget "Battery Life" from the marketplace. Because it has the option of showing the voltage, I like it very much considering it has only a 4 star rating. Looking at my widget right now, I am getting a reading of 3938 mV or 3.938 volts. My battery meter says 80%. Are you still with me? Our battery is 3.7 volts. Why is mine 3.9 volts? Well, the reason for that is because it is at the high end of the discharge curve. I wouldn't be surprised if it was 4 volts fully charged. When it drops to 3.4 or 3.35 volts, then I know, "ok, its getting low now."
I see people say, "I just watched 2 video, sent 5 sms and made 1 phone call. Why is my battery at 80% already?! Help!" all the time. My guess is that these "widgets" set it's bar when a battery is hot off the charger. A
lithium-ion battery will quickly sag in voltage under immediate usage. This is very common! The problem with most of these widgets is how high they set the bar.
Having said that, I get about 1 full day of fair usage. I do think the Moment could be more energy efficient but this is the price you pay for an 800 mhz processor. In all honestly, i think 1440 mAh is way too low for a smartphone. At least 2AH should be the standard. This is coming from someone that knows a little bit about batteries.
Considering the sharp voltage drop of lithiums due to it's high discharge curve, I'd say our battery actually has 4.8 or 5 watt hour of total energy instead of 5.328 wh.
When your phone "dies", your battery is not technically dead. If you were to completely drain that 5.328 wh of energy in your Moment battery, than it would really be dead. As in, dead as a doorknob dead.
The reason your(our) phone dies when we are low on battery is because the battery hits a low voltage cutoff or LVC. In order to preserve the health of a battery, it is important to keep it above the LVC. discharging and going below the LVC can have a serious affect on the battery. Going just a little under can degrade the life cycle by half and going way under can effectively KILL the battery.
Most phone (our's included) keeps track of the batteries voltage and auto shuts off when the battery dies. Even had a phone die on you and it powers down, showing the shut down animation? This is the phone's LVC at work. If the phone did not have a LVC, it wouldn't boot down at all. No fancy animation, it would just work until it dies. Just as if you were using alkaline batteries to power a mini fan. The blades of the fan would just move slower and slower until it dies.
The important thing to realize is that our battery's "fuel" meter is not linear because the voltage is not linear in a lithium-ion battery. In comarison, SLA batteries have a fair straight discharge curve. SLA's are strongest when fully charged and their power decreases after continuous use in a linear time. After continuous use, SLA voltage drops continuously. Think of it as an easy hill. From the top, you gradually coast to the bottom in a straight line. Whereas a lithium-ion battery usually have a high curve were the "hill" is a flat grade until you fall off it's cliff.
I hope this clarifies a few things.
. I still think this chemistry is not reliable for mass marketing. A BMS takes room and it's a hassle to deal with.