Battery Charging

The following is a response from a reader regarding battery charging….

Thank you so much for your question. It is a really good question. Your question just to restate is:

“If I charge my phone when it is at 50% capacity to full 100% capacity, would it be the same "1" charge as if I charged it from 20% to 100% capacity?”

To answer your question completely and to avoid confusion I will start with the basics and work my way to an answer for you!

To begin with battery capacity is a reference to the total amount of energy stored within a battery.  It is a mathematical calculation to determine how long a battery will run (power a device) before the battery “dies”. Battery capacity is rated in Ampere-hours (Ah), which is the product of: Ah= Current X Hours to Total Discharge.

As with all metric measurements, Amps can be divided into smaller (or larger) units by adding a prefix. For example a milliAmp hour (mAh) is most commonly used capacity notation on small batteries. A small battery that is rated 1000 mAh can be rewritten to read as 1 Ah.

Secondly, Amp hours do not dictate the flow of electrons at any given moment but instead measures remaining electron flow per charge. Amperes (Amps ) is a measurement of quantity of the number of electrons passing through a given wire per second. For every second your battery is on Per second there are 62,000,000,000,000,000,000 electrons passing through your battery. This electron flow, once started will never stop even if you disconnect your battery from your device and is the primary reason why batteries in time “die”.

You see when you charge a battery what you are technically doing is introducing electrons into the batteries chemical housed inside the battery cell. This electron introduction is called intercalation. Intercalation is the joining of a molecule (or molecule group) between two other molecules (or groups). When it comes to charging your battery you are in effect pushing ions in and out of solid lithium compounds (or other chemical types). These compounds have minuscule spaces between their crystallized planes for small ions, such as lithium, to insert themselves from a force of current (i.e. wall or car charger). In effect ionizing the lithium loads the crystal planes to the point where they are forced into a current flow. The current flow is then channeled back and forth from anode to cathode and thereby creating an electrical flow to power on your device. This flow can never stop once started.

Intercalation is the process that creates the electrochemical reaction inside the battery and allows the battery to replenish electrons as the battery is used. It is in essence the catalyst to move chemical compounds. This normal and how batteries were designed.  To move a chemical (lithium-ion, lithium polymer, lithium iron phosphate, etc) you have to have a minimum voltage applied. Most small battery cells are charged to 4.2 volts with relative safe workings at about 3.8 volts. Anything less than 3.3 volts will not be enough to charge or move the chemistry.

Now when we ask how long will my battery “last” we have to know that battery life varies depending on device configuration, model, applications loaded on the product, power management settings of the product, and the product features used. In addition to usage patterns battery life decreases every time you replenish electrons (i.e. charge your battery). This is called battery degradation and power loss and this is simply the normal use of any battery. Battery degradation and power loss varies with each battery and when it occurs it simply means that your battery has reached a point where it can no longer accept a charge and recharge the chemical inside your battery.

There are five overarching factors that govern battery capacity and they include:

  • Physical Size – the amount of capacity that can be stored in the casing of any battery depends on the volume and plate area of the actual battery. The more volume and plate area the more capacity you can actually store in a battery.
  •  Temperature – capacity, energy store decreases as a battery gets colder. High temperatures
    also have an effect on all other aspects of your battery.
  • Cut off Voltage – To prevent damage to the battery and the device batteries have an internal
    mechanism that stops voltage called the cut-off voltage, which is tpically limited to 1.67V or 10V for a 12 Volt battery. Letting a battery self-discharge to zero destroys the battery.
  • Discharge rate – The rate of discharge, the rate at which a battery goes from a full charge to the cut off voltage measured in amperes. As the rate goes up, the capacity goes down.
  • Battery History – Deep discharging, excessive cycling, age, over charging, under charging, all
    reduce capacity. Note charging your battery 1 time will reduce capacity as much as 15%-20% depending on your battery's chemistry.

Now with all of the above laid we can look at your original question with greater understanding.  Your question was:

“If I charge my phone when it is at 50% capacity to full 100% capacity, would it be the same "1" charge as if I charged it from 20% to 100% capacity?”

We know that the life of a lithium based rechargeable battery operating under normal conditions is generally up to 500 charge-discharge cycles with the maximum capacity decreasing with each charge-discharge cycle. NICD or NIMH batteries can last up to 800 charge-discharge cycles

Charge-discharge cycling a battery means to completely discharge (or drain) a battery’s created electricity to where there is a charge of less than a 1% capacity remaining. At this point the power to the device will cease and your device will power off. Then after the power is off you recharge the battery to 100% capacity using a power adapter from a wall socket for example. Regardless of how you charge the battery that process of discharging and charging represents one complete charge cycle.

A battery in generally can have between 300-500
charge-discharge cycles (for lithium based chemistries – NIMH can have up to
800 charge-discharge cycles and NICD chemistries can have more). A
charge-discharge cycle means that a battery once at 100% draws power down to
0%. Then after recharge it will be back at 100%. This can be done 300-500 times
on the same battery. Also with each charge-discharge cycle the runtime (time
between charges) is reduced by the gradual depletion and usage of the battery's
chemistry inside. For example you may notice in the first 3-4 months you are
getting between 3-5 hours of runtime on your battery. Then in month 5-12 (after
your purchase) you notice that you are slowly getting less and less runtime in
between charges. This is the normal use of the chemistry inside your battery
and DOES NOT mean that the battery is bad or defective, but simply has been
used by you.

Now one complete charge-discharge cycle means that you draw your batteries capacity (the abiltity to run your battery) from 100% down to 0%. If you draw the battery from 100% to 50% capacity then recharge the battery back to 100% that would represent ½ a charge-discharge cycle. Now technically this is different than running your battery from 100% to 20% then recharging.

Now if you plug your device in 4 times a day to recharge it whether it starts at 20% or 90% then each recharge would be some percentage of one complete charge-discharge cycle. Again each complete charge-discharge cycle does degrade the lifespan of the battery by a small percentage. 

Now one thing that should also help is that inside your battery are integrated power management circuits that protect your battery and device against over-voltage and under-voltage conditions. The power management circuits also maximize battery life between charges, minimize charging times, and improve overall battery life. So no need to worry about leaving your battery on your charger – when the battery is done charging it will simply stop accepting a charge!

Now keeping all the above in mind does it make sense to keep your device plugged in continuously if each charge-discharge cycle does degrade the lifespan of the battery by a small percentage? Each person has to make their own conclusion to that question. If your battery is near the end of its useful life then of course you will find that you must constantly recharge your battery but if your battery is new then it does not need to stay on the charger as frequently. I typically wait till my battery is almost dead before I recharge unless I know I will be away from any means of charging the battery. By the way a really cool device for recharging a battery is the Universal USB Battery Pack. It conveniently stores 5600 mAh of portable power to charge your mobile devices anywhere, anytime. It includes 8 connectors, USA and Europe adapters, plus universal USB charging cable. This is awesome!

I hope this helps answer your question! Thank you and Happy New Year!