If you want to be super paranoid about battery wellbeing, here are some expanded points I posted in another thread that we could modify/add to. Many relate just as much to safe operation as they do prolonging life, as the two things are often complimentary.
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The battery
will wear no matter what - whether you use it or not. Given the cost of replacement is not terribly high, the lifespans are reasonably long, and AppleCare covers replacement, IMO the best thing one can do is enjoy it and not allow worry over battery health to cause modifications to usage patterns that cause tremendous inconvenience. At the same time, a basic understanding of lithium cells provides the User with the basic knowledge needed to maximize the lifespan (and safety) of
any portable devices powered by rechargeable lithium batteries.
I'm far from an expert here, but here are some things to keep in mind that applies to LITHIUM cells...
- Many of the basic handling/usage/charging/care/safety guidelines that apply to NiMH and NiCad rechargeables are NOT the same with lithium rechargeables. - For example, where as NiMH and NiCad can be used safely with continuous trickle charging (although this is not optimal for longevity), lithium charging must terminate at a specific voltage (often 4.2v) or else they can enter a dangerous state of overcharge, sometimes ending in a vent-with-flame (i.e., it ends with what most people would essentially call an explosion, and when a lithium cell vents it can set other things on fire.) Cheap lithium chargers/batteries carry an inherently greater risk because, should the charger fail to terminate charging at the correct peak voltage, and, should the battery's protection circuits fail to break the connection to a malfunctioning charger (or should the battery not have its own protection circuit at all), the battery could continue to charge right up until it vents-with-flame. (This has happened quite often in the world of eCigarettes, where someone uses a terrible quality 'super-fast' charger, a terrible quality battery, and it ends badly
.) Further, crappy chargers may attempt to charge a severely over-discharged battery, and crappy batteries may have crappy protection circuits that allow the battery to be recharged even after an extended period of over-discharge (this is hazardous and can end in a vent), and crappy batteries/chargers may fail to detect early signs of thermal runaway from other causes (also hazardous and can end in a vent.) The stakes are arguably higher here, and the efforts made towards safe operation are sometimes lacking when considering the risks.
- If convenient, recharge your battery once it hits around 75% - Light discharges place less wear on the battery than deep discharges, and lithium cells do not have a memory effect. If you use the battery frequently and only run it down say from full capacity to three-quarter capacity and then recharge, this places little wear on the battery and in some cases may prolong life more than simply leaving it in a constant fully-charged state.
- Frequently running your battery down to the point of being near empty will shorten the service life significantly - Deep discharges place a huge amount of wear on lithium cells. For example, running the battery down to only 5% remaining capacity and recharging it just one time could place more wear on the battery than running it down to 75% capacity and recharging it 10, 20, or 30+ times. Apple cycle counts DO NOT REFLECT THE SPECIFIC DEPTH OF DISCHARGE! Consequently, cycle counts say only a limited amount regarding battery wear.
- If your computer is usually plugged in, occasionally running it down to 75% capacity and recharging may extend its service life - Long periods at fully charged capacity causes wear because at 100% capacity, the battery is at its maximum voltage (for example, 4.2v/cell), which is higher than the nominal voltage (for example, 3.6 or 3.7 v), and this places stress on the battery. A battery that is never used and always fully charged will still wear even without usage.
- Leaving your battery at extremely low or empty capacity is one of the worst things you can do, and doing this often will rapidly reduce the battery's service life - Long periods at very low capacity causes rapid wear - in some cases, this can destroy the battery.
- Frequently storing your laptop in a hot car or sitting in bright sunlight will dramatically shorten the lifespan - Heat expedites wear and it is arguably the biggest single enemy of lithium cells (ironic, right?)
- There is no such thing as a "calibration discharge" or "battery calibration" on modern Apple laptops with OEM internal batteries - running the battery all the way down on a set schedule wears the battery and may not improve reporting accuracy anymore than a SMC reset. (Note that some third party companies that sell 3rd party Apple-compatible batteries advise performing calibration discharges.)
- Applications that report on battery health statistics are not necessarily accurate. Further, the metrics that the battery reports (such as a health %) can fluctuate somewhat on a day-to-day basis - The value of these battery metrics are IMO limited, and the biggest single indicator of battery health should be the real-world runtime.
