Q: Is it true that I should let the batteries on my laptop and smartphone run down all the way before I recharge them in order to extend the life of the battery? - Skip
A: Today's mobile electronics are capable of doing some amazing things greatly due to the major advancements that have been made in battery technology.
Most of today's mobile electronics use Lithium-Ion batteries, which are substantially better than the older Nickel-Cadmium (NiCad) and Nickel metal hydride (NiMH) technology.
Lithium-based batteries can store more energy in a smaller package, they don't dissipate energy as quickly when the device is not being used, they can handle more charge cycles and they are capable of charging up quicker.
Nickel-based batteries were susceptible to ‘memory' issues when charging, so the general rule was to always run the battery down to near 0 before recharging.
Lithium-based battery systems don't have this memory charging issue so this practice is unnecessary for today's devices (constant full discharges can actually accelerate capacity loss in lithium ion batteries, so keep the full discharges to once a month if possible).
For devices that have a ‘gauge' (such as laptops) it is a good idea to let the device run all the way down every 30 charges so that the gauge can recalibrate itself.
This will help keep the gauge accurate so it can properly represent the amount of power left.
All batteries have a finite life, generally based on the number of times it's been recharged (often referred to as charge cycles).
Apples website explains how the charge cycles are calculated:
"A charge cycle means using all of the battery's power, but that doesn't necessarily mean a single charge. For instance, you could listen to your iPod for a few hours one day, using half its power, and then recharge it fully. If you did the same thing the next day, it would count as one charge cycle, not two, so you may take several days to complete a cycle. Each time you complete a charge cycle, it diminishes battery capacity slightly, but you can put notebook, iPod, and iPhone batteries through many charge cycles before they will only hold 80% of original battery capacity."
You can expect 300-500 charge cycles from lithium-ion batteries before a noticeable decline in battery life occurs and technically they prefer a partial discharge over a full discharge on a regular basis.
Heat is actually the biggest factor in the life of any battery. The more heat it encounters, the quicker it will degrade. Leaving your battery powered devices in a hot car or trunk or in direct sunlight on hot summer days will do more to kill the life of the battery than anything you do in the charging process.
Never turn on or try to charge a batter y that has been sitting in a hot environment; always allow it to get back to room temperature or you will reduce its life (and do everything you can to avoid the high heat situations altogether).
Although most recharge systems have an auto shutoff to avoid overcharging, as a precaution, try not to leave a fully charged device attached to the charger for extended periods of time (especially if you can feel that the battery is hot).
If you are not going to use the device for an extended period of time, the best way to store it is with a 40% charge and in a cool place (like your refrigerator). Lithium-based batteries prefer to be cool and will generally last longer in colder climates and when they are partially discharged on a regular basis.
Another thing that can help extend the life of any battery is slower charges (lower voltage), so smartphone users may want to consider charging their phones via a USB port on their computer throughout the day when possible.