In rechargeable lithium-ion batteries – the most common type, used in things like laptop computers and cell phones – one of the two electrodes is graphite, a form of pure carbon consisting of sheets of carbon atoms.
Lithium ions are forced between the carbon sheets when the battery is charged and come back out again when the battery is discharged, explains Robert Hamers, a Wisconsin Distinguished Professor and chair of the UW-Madison chemistry department.
“The first few times that a battery is charged, a chemical reaction occurs on the graphite, forming a thin protective layer,” Hamers says. “Over time, this layer slowly becomes thicker and eventually begins to block the flow of electrical current needed to charge the battery, degrading the performance.”
A second reason the storage capacity diminishes is physical wear of the graphite itself, he adds. “There is a large volume change as the graphite expands and contracts. Over time that causes the graphite to flake and small particles to break off.”
In nickel-metal-hydride batteries, the second-most common rechargeable battery, a small amount of water helps carry electrical charges between the two electrodes. Each time the battery is charged or discharged, side reactions convert some of the water to hydrogen and oxygen, which slowly leak out of the cell. When there is not enough water left, the battery dies.
1. Battery Memory – When I first got my new cellphone, my friend recommended to fully drain the battery before recharging it. His reasoning was connected to the idea of battery memory. Allowing the battery to fully discharge then recharging to max, supposedly gives you the complete battery capacity. Otherwise, if you simply charged from the half way point to max battery capacity, the battery would treat the half way point as the empty point, thus cutting your battery capacity in half.
The good news is today’s lithium batteries have a safety circuit in place to insure the battery doesn’t reach the point of no return. The safety circuit isn’t fool proof though, if you leave your battery completely drained for a few days, even the circuit’s protective measures won’t save it.
2. Battery Calibration – There are some benefits to fully discharging your lithium battery periodically, for laptops this can be especially important. If you start to notice your battery meter becoming more and more inaccurate, it may be time for some battery calibration. Allow your lithium battery completely drain, then charge until the battery is full again. This will calibrate your battery giving you more accurate readings. This should be done once every 30 charges or when you notice battery readings are off.
3. Consequences of Heat – Another enemy of lithium battery life is heat. If you were to leave your laptop plugged in and running for a year, you should expect the lithium battery capacity to be anywhere between 60% to 80% of it’s original max capacity. This is why people that use their laptops as desktop replacements will notice greatly reduced battery life performance after one year of use. This issue can be resolved by removing the battery while using a corded power source. Now you may want to check with your manufacturer ahead of time to check for safety concerns, some manufacturers have mentioned problems such as moisture and dust collecting in the battery casing.
4. Battery Storage – If you don’t plan on using your lithium battery for prolonged periods of time, then you’ll want to reduce the charge level to 40% and place the battery in the fridge (not freezer). Storing the battery at 100% charge level applies unnecessary stress and can cause internal corrosion. On the other hand, if the charge is too low, the battery can become permanently unusable, due to battery self discharge. This is why manufacturers recommend storing your lithium batteries at 40% charge, rather than either extreme.
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