I recently bought a new laptop and the store person told me that I needed to fully discharge my battery before recharging it as a method of calibration (so my PC would know what % of energy was stored).
Also I’m told that I should discharge fully my cell phone battery once every month or so to get the best results from a fresh recharge.
Can anyone tell me why I should have to do this?
Is it a chemical reaction in the batter that stops me from getting the full capacity until it’s fully discharged?
Pretty much what the store person told you; battery charging on many electronic devices is now controlled by software or firmware in the device itself; when the battery voltage drops below a certain level, the device will sense it and start recharging, but with some laptops (mine included) and certain types of battery, the relationship between voltage and remaining charge changes over the life of the cells, so the machine might be showing the battery as flat while there is still a fair bit of usable charge in there. My laptop has a battery calibration utility that essentially turns off all of the emergency hibernation stuff and charges the battery fully, then runs it until it actually dies - thus measuring the actual voltage/remaining charge graph.
Most rechargeable batteries have a “memory” effect.
For the longest service life and efficient useage the battery should be fully discharged periodically. For daily useage it shoul not be recharged until it is really getting low and about to the point of not providing service.
In other words don’t recharge it when it shows a 50% or 75% charge!
A battery that is recharged repeatedly at 50% or 75% will soon not be able to take a full charge due to the “memory” effect.
You probably shouldn’t do this with lithium ion batteries at all, since they slowly lose capacity with each cycle, and nobody’s ever accused them of having a “memory effect”. Most new laptop and cell phone batteries are lithium ion.
More specifically, it’s an effect that occurs only in batteries which undergo a very regular charge/discharge pattern, and even then it proved difficult to replicate in the laboratory. Even satellite batteries (most of which even today are NiCd types), which undergo about as regular a charge/discharge cycle as is possible rarely exhibit a memory effect. What most people call “memory” is actually a loss of capacity due to overheating or overcharging. This is especially prevalent with the use of so-called “rapid chargers” whcih can considerably shorten the lifespan of NiCd and NiMH cells. True NiCd memory is similar in symptoms, but the cause is very different. There is a good article on the Repair FAQ about NiCd memory.