Primer on Battery Charging iDevices and MacBooks as of Dec. 2013

Primer on Battery Charging iDevices and MacBooks as of Dec. 2013

There are now several types of rechargeable batteries, all of which have different optimum charging properties. The three most common for small electronic devices are. Nickel-Cadmium - NiCd, Nickel Metal Hydride - NiMH, and Lithium Ion - Li Ion. (Lead Acid and Gel Cells  are not covered here).

NiCd has the memory issue that if not perfectly charger on a regular schedule and then discharged similarly, they tend to have molecules stick permanently to one plate and produce lower and lower voltages until they do not work well enough to use. They work best in cordless phones and razors or toothbrushes that rest in their charger.

NiMH are similar to NiCd but more environmentally friendly. They are lighter and have found use in cell phones BlueTooth devices etc.

Li Ion (Lithium Ion - not the same as non rechargeable Lithium) are a newer plate and chemical concept that requires higher per cell voltages and delivers more power for the weight while still lasting for many charge cycles, they also hold charges longer between uses. Power tools and many Apple products use these.

Basically charging a battery moves molecules from one plate to the other plate inside the battery. (there are actually many plates and chemistry involved to intensify this process to make enough current to be useful). Discharging reverses this process. Charging requires slightly more voltage from the charger than the battery supplies (thats why a car amp gauge shows 13.7 volts while charging a 12 volt battery). It also requires that the charger have enough current available to overcome the resistance internally in the battery to this change in molecular particulate location. The Current and Voltage need to be controlled to avoid accelerating the chemical and physical changes to the point of ignition (exploding or catching fire).

Batteries supply energy in the form of voltage and current. Devices all have different needs based on Power, Weight, Longevity, Temperature and Size.

Current can be thought of as the the size the hammer needed for the job, while voltage can be considered as the length of the swing. Both affect the results of the use of power.

A small device requires a small hammer and light weight hammer taps of energy (an iPod). Al large device may require a Sledge Hammer with a John Henry size swing (a 12 million candle power flashlight)

To Optimize the life of the battery, the discharge rate and recharge rate should be similar. If you drive a 16 penny nail into a piece of Oak with a sledge( a high powered charger), it will take a long time to pull it out using a pair of tweezers (an iPod). The reverse is also true, Tapping a 16 penny nail into a piece of Oak with a tiny hammer (a 5 milliamp charger) would take forever, while removing the nail with a crowbar (a 1000 Milliamp Portable amplifier) would only last seconds.

These extremes are abusive to batteries as they move the molecules to quickly and with too much force which causes heat and damages the surface of the plates and destroys the chemistry inside the battery by baking it.

Hi Quality products that use batteries usually come with a charger designed to replace the power at precisely the right rate to give the battery the best chance of lasting a long time with out damaging it by over charging and causing heat, a battery's worst enemy.

Our smaller devices require less current (smaller hammers) and usually between 3 and 9 volts and less than 500 Milliamps -ma). Our larger devices usually require 12 volts (and more than 500 ma.)

Apple has universalized their iPhones, iPods, iPads by using 5 volt custom built batteries for each device, but each has a different current requirement based on the work it does. The iPod uses the least, the iPhone uses more because of it's transmitter for the phone part, the iPad uses the Most because of its screen size and Processor and Graphic chip requirements. Anytime a transmitter gets involved current requirements go way up - Blue Tooth, Phone Pings/Talk time, AirPlay, wireless WiFi. This is why we have so many hours of "Standby" or music, but few of Talk and WiFi or AirPlay to an Apple TV. MacBooks are another story as they require much larger batteries and higher voltages to meet design standards for computer circuitry, which seems to be in the 12 to 24 volt range. Portable computers draw substantially more current at higher voltages than iDevices and therefore require bigger and stronger power supply/chargers. The draw is so high that they require fans to keep their insides cool when maximum processor, display power is being used (Motion Graphics-Video-Wireless internet-streaming and such). But, the charging and battery processes are the same, just bigger.

Building a low priced charger to fit all these batteries is not easy. It requires several additional circuits inside the charger to limit current and voltage, yet supply enough to charge the battery. Note that in order to actually charge a battery the applying device must have a slightly higher voltage (Hammer swing to beat the nail in) than the battery, but as it approaches full charge the voltage needs to drop (gradually) to equal the battery voltage to avoid over charging. This too, requires circuitry to match the battery properties (Size, current, voltages) without overcharging.

Now you know why Apple makes their own batteries and chargers. Each is matched to the device for "Optimal" battery life. It's true you can use a 2.1 Amp (2100 ma) Apple charger from an iPad on an iPhone and it will charge slightly faster (and it will not damage the iPhone) because Apple has added current limiting circuitry to it's iPad charger specifically for this purpose. It's also true that you can charge an iPad with an iPhone charger (1000 ma) but it will take longer and may not be able to fully match the value of the 2.1A charger (smaller hammer with the big nail cannot completely match the bigger hammer). This usually makes the iPhone charger hot, since it it working hard and long at full output trying to meet the iPads needs.

Third party vendors have the choice of adding this delicate circuitry (without inside knowledge of Apples Battery engineers) or ignoring it and just making a cheap unregulated charger. Using an unregulated charger on an iPad battery dumps full current into the battery until it is disconnected. This usually results in overheating the battery and shortening its life (chemical and plate destruction) "Fast" chargers also shorten battery life (Charge cycles) by over doing the charging process only slightly. This does not immediately ruin the battery, but will reduce charge cycles. Cell phone fast chargers do this on a regular basis and users blame the battery (incorrectly) for not lasting.

Without benefit of scientific electronic testing equipment, testing batteries and chargers is impossible. Individual recommendations are made based on incomplete information and what worked for one individual and their circumstances and also observations which are many times true but inaccurate based on limited use and time frames.

There are third party companies that try very hard to make quality chargers for Apple products but Apple does not freely give out the specifications on their proprietary batteries that they have spent millions developing. So, buying even a High Quality expensive third party charger will not guarantee it will be "better" than Apple's. However, that said, there are other reasons one may want a third party charger. Small and low priced for vacation or travel use, why forget an expensive charger in a hotel room? Charging many devices at the same time from one charger, for those that charge everyday and take multiple devices on the road as part of their business life. An occasional quick charge in an emergency. These are justifiable reasons and will do minimal battery damage if used as intended.

These are just the basics surrounding rechargeable batteries for Apple products and how they select batteries for each individual device based on making the overall experience the best they can. There will always be cheaper and better options, but Apple usually gets very close to the center of the target on most decisions for their products.