I recently purchased a new cell phone, and the retail agent advised me to charge it for 3-4 hours, then allow it to drain, and then give it a full charge overnight. I was relatively aware of this procedure, but I had always thought the proper protocol was to give the battery a full discharge followed by a full charge to maximize performance. Clearly some research about the current state of battery technology was in order.
Nowadays, all portable electronics use Li-Ion batteries. The current state of Li-Ion technology has made Nickel batteries fairly obsolete. There are some circumstances where Nickel batteries are appropriate, but in general the weight and performance if Li-Ion batteries make them superior for use in portable electronics.
My new cell phone is no exception. So the question is: what is the proper way to first charge a Li-Ion battery and then prolong its life. Fortunately for us, Li-Ion design today is fairly foolproof. Li-Ion is a clean charging system and does not require any priming; therefore, any instructions to charge, discharge, etc are relics from when Ni-Cd batteries were the norm. The only real advantage to giving your battery a full discharge and recharge is that it will reset the 'state of battery' estimation for a smart battery. So, if your battery begins to read empty yet continues for function for a long time or vice versa, giving it a full discharge and recharge will reset the meter properly.
Moreover, Li-Ion systems protect themselves from overcharge, so leaving them plugged in should have no detrimental effect. The battery will automatically give itself a topping charge once every 20 days or so. Unlike nickel systems, Li-Ion batteries have no trickle charge and keeping them plugged in is relatively safe.
So what exactly can you do to prolong battery life? Li-Ion batteries actual perform better under a partial charge, and charging to 3.92V rather than the rated 4.2V can double your cycle life. On the other hand, you will inevitably lose some capacity, and who really has the time to unplug their cell phone shortly before it's fully charged. Current battery technology has advanced to the point that typical Li-Ion cells can last 300-500 full cycles. Estimates equate this to about two years of normal usage.
That being said, you can improve on these numbers by following specific charging protocol. The simple rule is to charge where and when you can. Li-Ion batteries are designed to to perform the best with a partial charge, so the less time they spend discharging the better. This simple study compared charging overnight, charging when empty, and charging whenever possible:
http://blogn95.blogspot.com/2007/07/gentlemen-charge-your-batteries.html
The results: Charging overnight and whenever possible far outperformed the charged on empty battery. That really is the simple rule. Don't worry about priming your battery. The first time you charge your battery is no different from every other time for Li-Ion batteries. Just try to charge it whenever you can, and that will effectively maximize battery capacity and life.
Additional Sources:
http://www.batteryuniversity.com/partone-12.htm
http://www.batteryuniversity.com/partone-21.htm
http://www.batteryuniversity.com/parttwo-34.htm
http://vidmar.net/weblog/archive/2004/06/11/308.aspx
Sunday, July 19, 2009
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