Q: I’m considering getting the new third-generation iPad, but I’m worried about how long it takes to charge. I know it’s normally a good idea to let the battery run down a lot before plugging my device into a charger, and with my iPhone that’s actually never a problem because it’s almost dead by the end of the day anyway. However, I’m concerned with the iPad being too low when I actually need it and then taking 6+ hours to recharge before I can use it again. I don’t want to shorten the battery life by plugging it in all the time when it doesn’t really need it, especially since I’ve heard it keeps charging all the time even after it’s full. Is this really likely to be problem or am I just worrying too much?
– Geoffrey
A: Not only are you worrying too much, but you’re also falling victim to some common misconceptions about rechargeable batteries in modern electronic devices such as the iPad.
Firstly, the whole issue of “overcharging” has actually been debunked as a myth in our own independent testing here at iLounge, so there’s no need to worry about that issue at all.
Beyond that, however, there is also no reason whatsoever that you need to be concerned about plugging your iPad in to charge whenever it needs it, regardless of the actual charge level. Lithium Ion batteries don’t suffer from the “memory effect” that was common with older rechargeable batteries, and in fact actually prefer to be “topped up” on a regular basis.
We actually wrote about this in more extensive detail back in May 2008, however four years later little has changed and the previous answer still applies to the iPad in the same manner as any of Apple’s other portable devices:
The first and most important consideration is that the majority of modern electronic devices with rechargeable batteries now use “Lithium Ion” batteries (Li-ion). Unlike earlier generations of rechargeable batteries which were based on Nickel Cadmium (NiCad) or Nickel Metal Hydride (NiMH), Lithium Ion batteries do not suffer from the “memory effect” when it comes to recharging. Previous Nickel-based rechargeable batteries, particularly NiCad batteries, would lose their maximum charge capacity if they were not fully discharged prior to charging them up.
Li-ion batteries, on the other hand, actually prefer to be topped up, and should never be completely discharged, as this will actually destroy the battery. Most electronic devices, including the iPod, have a cut-off circuit that turns the device off when the battery drops critically low in order to prevent this from happening, thereby leaving a small charge in the battery, so this is rarely a practical concern for an end user.
Likewise, while lithium-ion batteries can technically experience problems from overcharging (continuing to charge the device after the battery is fully charged), any properly-designed electronic device will incorporate a “cut-off” circuit to stop charging the battery once it’s reached its full charge level in order to prevent this.
Another point to note is that there is no requirement for a lithium-ion battery to be “primed” before use. Recommendations that a new iPod be plugged in and charged overnight before using it for the first-time are based on older nickel-based battery technology. For a Li-ion battery, there is no difference between the first charge, the tenth charge, or the 100th charge.
The life expectancy of a lithium ion battery in terms of how many charges it will take is measured in “charge cycles” which refers to the number of complete discharge and recharge cycles, not simply to the number of times the battery is “topped up.” Therefore, if you drain your battery by 25% and recharge it fully four times, this will count as a single charge cycle. Again, there is rarely a reason for the average iPod user to worry about watching the charge level or being concerned about reaching a certain level before recharging—simply dropping the iPod into the charger whenever necessary is fine.
In fact, the only reason in the case of an iPod for doing a complete discharge and recharge of an iPod is to re-calibrate the battery meter itself (ie, the iPod’s display of how much power is remaining). This has no impact on the actual battery life, but will help the iPod provide a better estimation of the remaining life for the user by ensuring the battery gauge is accurate.
In terms of how the charging process itself works, Li-ion batteries charge in two stages: If the battery is below approximately 70-75% charge level, the first stage involves applying full charging power to get the battery charge up to that level. Once the battery reaches the 70-75% level, a “topping” charge is applied, whereby the current to the battery is gradually decreased as the battery capacity reaches 100%. This is done in order to avoid overcharging, and is sometimes referred to as a “trickle” charge, although this is technically incorrect by definition, since a “trickle charge” refers to continuous power being applied to a battery once it has reached full charge, which Li-ion batteries do not do, again in order to avoid the risk of overcharging.
With a Li-ion battery, once full charge has been reached, the charging circuit will shut off completely and stop providing any charge to the battery. At this point, as long as the device remains connected to external power, the battery goes dormant and the device simply runs from the external power source. What this means for the iPod is that as soon as you see the “Plug” icon on the battery indicator, charging power has been cut-off and the device is simply running from the external power source.
If you leave the iPod connected to an external power source for long enough, the battery will drop slightly in power just from normal energy loss (in the same way that it would if it were simply sitting on a shelf turned off). Once the battery falls below a certain level, a topping charge will be reapplied to bring it back to full, but this normally happens very infrequently as long as the device remains connected to external power—possibly as rarely as only once every three to four weeks.
Disconnecting the iPod from external power and reconnecting it will re-initiate the charge circuit, since the battery level needs to be re-checked, and a small topping charge may need to be applied to get back to 100%, but unless the device has been used on battery, the iPod should return to the plug icon within a few minutes, once again indicating that the battery is fully charged and the device is running from AC power. In many cases no topping charge is applied, and this delay is just the time it takes for the iPod to resolve that the battery is, in fact, fully charged.
The net effect of disconnecting and reconnecting your iPod from its dock should be basically neutral in terms of battery life. The topping charge is applied only to bring the battery back to 100%, so this is a fraction of a battery cycle in the same way as any other charge.
Unfortunately, many of the now-outdated issues with nickel-based batteries have become urban myths for modern electronic devices, and can cause many iPod owners much completely unwarranted angst about their device and their battery life. In reality it is almost never necessary for a typical iPod user to worry much about the iPod battery… The simple rule of thumb is to use the device as you normally would, charge it when it needs it, and don’t worry too much about leaving it on the charger for reasonable periods of time.
In fact, just about the only issue to be aware of is for those rare users who use their iPod from external power all the time. In this case, since the Li-ion battery is not being used (the device is running from external power), the battery itself doesn’t get properly “exercised” and this can decrease the battery life over time. This is only an issue for users who almost never run their iPod from the battery. Apple’s own support site simply suggests that the battery be put through at least one complete charge cycle per month. Considering that even twenty 5% “top-up” charges still counts as a charge cycle, the reality is that for the vast majority of iPod users, normal everyday use will easily take care of this.
