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#1
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Jimmy
03-15-2012 10:54 AM

lithium polymer battery life info

I'm having problems looking for info on Google for battery life of a "31-watt-hour Lithium-polymer battery"

does anybody know how long on average do these batteries last compared to normal 4/6/8-cell Lithium batteries? And also are there any special care required for them?

I've heard somewhere that Apple Macbooks also use the same battery, but they have a higher wattage (36-watt or something) and can last up to about 3-4hrs on average... Can anybody confirm this?
03-15-2012 10:55 AM
Top #2
Fellis
03-15-2012 10:55 AM
just to clear up a bit of theory, hopefully it will help your search for information.

a Joule is a unit of energy.

A watt is a unit of power. It tells me about how quickly I consume energy. A watt is one joule per second. If i use energy quickly, i am powerful.

a watt-hour is also a unit of energy. One watt (one joule per second) for one hour is one watt-hour. You can convert watt-hours to joules by a factor of 3600.

now batteries/cells are usually measured in watt-hours. This isn't the be all and end all of battery measurement because the apparent watt-hours varies depending on the load. Neverthelss I'm not going to complicate things by discussing the non-linear nature of cells.

If I have a 36WH battery of which I am draining at 10W, It will last 36/10 = 3.6 hours.

So, to answer your question about a 31WH battery, I need to ask the question: what is your current draw? This will tell me how long your battery will last.

To increase the watt-hour (energy storage ability) rating of a battery you have more cells (more simultaneous reactions) If a cell provides me 6 Watt-Hours, two cells will give me 12 watt-hours. Three cells will give me 18 watt-hours.

So we choose batteries on a few factors:

energy density (how much energy we can store into a small space)
price!
characteristics of that reaction. Li based batteries have a considerably reduced memory effect compared with nicd or nimh batteries. your car uses a lead-acid battery because it needs to provide large amounts of energy in a short time (high power). Think of a sprinter vs a marathon runner.

Don't worry too much about li-ion vs li-po batteries. Both are well suited a slow draw with high energy densities. Focus on WH which is related to cell count and the physical dimensions of the battery.
03-15-2012 10:56 AM
Top #3
Jimmy
03-15-2012 10:56 AM
that is a very handy piece of knowledge there – thanks!
This is a very good rough baseline to consider...

i suppose it doesn't matter if they are Li-Ion or Li-polymer, a 44Wh battery life will be the same as one another (all other things being equal)? Or in other words, a 44Wh li-io battery does not necessarily last longer than a 44wh li-polymer battery (and vice versa), yes?
03-15-2012 10:57 AM
Top #4
gooo
03-15-2012 10:57 AM
I put a power meter on my P4 ULV 1.2ghz 11.1" vaio.

charging the battery it was 14W running in full power (1.2ghz cpu) no battery management. When charged it dropped to 7W. With battery management on optimized (cpu @600mhz) fully charged battery it dropped to 5W.

That is the complete system running though.
03-15-2012 10:58 AM
Top #5
Denial
03-15-2012 10:58 AM
That is interesting. It suggests that running the laptop on battery will be around 5W. Do you have BatteryBar installed? That will show the power used when running on the battery (if the battery supports it). Other tools also report it, but that's the one I can think of at the moment.

I put a power meter

I really should get one of those.
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