Are you killing your battery?


Charge your battery for 8 hours before first use!

We have all seen that, right?… Of course we have.  Fact is that the warning has nothing to do with the lithium-ion batteries of modern phones and laptops and more to do with manufacturers simply not changing their text-based materials.  Modern lithium-ion batteries DO NOT need to be fully charged once they are in a consumer’s hands.  They were previously charged at the factory for the “first use” and don’t need a second go-around.  

What the label should say is:  Turn on your phone and play around… Make a few calls… Listen to some music… Sync your contacts and data…  That IS what we tend to do anyway, so they should really just let us know that it is okay to do so, and may actually be good for our batteries.

In fact, fully charging a lithium-ion battery that has been in storage before use COULD BE detrimental to its overall life.  It is better to use that charge that it had out of the box and then charge it up for the first time from or near to 0%.  There is a ton of technical jargon that I could (but won’t) use to explain why this is the case; instead, I’ll try to simplify it at the risk of being less than complete (and somewhat glossing over reality, in the same way that saying the 100 years war lasted 100 years)…



Imagine your battery to be a bit like a bowl of chicken noodle soup.  When it is warm and fresh, the broth is mostly clear.  As it sits, and becomes colder, an opaque crust layer develops on the top.  This layer doesn’t flow like the broth beneath.  Some lithium-ion batteries that have been in long term storage act somewhat like this… Some part of the ions seem sluggish and don’t want to charge as rapidly as others, creating a lower overall capacity.  Much like the soup example, the best way to get rid of the layer is to heat it up…

So… How would you heat it up?

By charging it.  BUT you want to heat it ALL up equally just like your soup.  You do this to soup by stirring; you do this to a battery by reducing the charge to the same level throughout the battery (0%) and then charging.   (Whether this actually happens is a debate for physicists.  Frankly, it just tends to work, so the mechanics don’t really matter.  After all, we still don’t know exactly how Benadryl works…)

Most lithium-ion batteries quick charge to about 80% and then trickle charge from 80-100%.  This quick charge generates a lot of heat, as you’ll notice when you pick up a charging phone.  If there is a crusty layer, it should dissolve, and your battery should have a fairly equal charge across all of its cells.

Given this, it follows that it is best to fully use your battery before charging it each time, right?  NO!  In fact, heat is the enemy of lithium-ion batteries in general.  Leave your phone in a hot car?  You are killing your battery…  Plop it on the dash while you are driving?  Killing your battery…  Always charge it from below 80%?  Killing your battery…

Back to the soup…

You have a huge pot of soup.  Each time you want a bowl, you put the big pot on the stove, set the burner to high and walk away.  Soon, it is boiling.  You dip yourself a bowl and turn off the soup.  Next time, same thing… And again, and again.  Each time it boils, you lose some of the liquid to steam, and the flavor diminishes as you boil it away… Over time, the soup doesn’t taste the same and you have less and less than you would have had…  

Same pot of soup…

Each time you want a bowl, you slowly heat it until it is just the right temperature, and remove your portion…  The soup will keep its flavor, and you won’t have lost much to steam.

Your lithium ion battery works somewhat the same way, in that small recharge cycles keep the capacity at the potential maximum, mostly due to the lower heat at shorter intervals.

But what about the battery developing a “memory?”

That sort of thing doesn’t really exist for lithium batteries like it did for the older Nickel-metal batteries.  It IS POSSIBLE for SOME “smart” batteries to need an occasional calibration, but it isn’t really the same thing.  Coincidentally, calibration is done just like the initial discharge to zero and recharge to 100%.  So, if you think your battery just isn’t charging like it used to, you can try a single discharge-recharge cycle.  It MIGHT work (but wouldn’t be necessary more than about once per year for most people).

In fact, it is better to charge your phone (or laptop) whenever you can…  Modern devices will stop charging when they reach 100%, then use the battery power until they drop to around 90-95% before they begin recharging again.  So, leaving your phone (or modern laptop) plugged in after a full charge isn’t really detrimental to its life.

Want to see some numbers?… No?  Well I’m going to tell you anyway…  


Cycle life as a function of depth of discharge.

Depth of discharge

Discharge cycles

100% DoD 300 – 500
50% DoD 1,200 – 1,500
25% DoD 2,000 – 2,500
10% DoD 3,750 – 4,700

A partial discharge reduces stress and prolongs battery life. Elevated temperature and high currents also affect cycle life.


Well, let’s break it down…

The common lithium battery if used to zero and recharged to 100% every day would last 300-500 days.

If it were half used and recharged every day it would last 1,200- 1,500 days.

And if only used 10% each day and recharged it would last 3,750-4,700 days.  

Since a “cycle” is 100%, then each 10 days would be one cycle for the 10% DoD.  Using the lowest 100% discharge numbers as a basis, and charging your battery from 10% 10 times each day, you might expect the battery to last only 10 times as long, or 300 days… Instead, there is an  extra 75 days or 25% longer life.  This happens because of the lower heat required to recharge the battery.

Now… This table is really just to show the detriment of full discharge on a regular basis.  The variables that occur with everyday life are just too many for me to tell you exactly how long your battery will last. Indeed, batteries vary immensely even within the same batch. And this table uses a constant charge rate to show the effects of heat.  In reality, a battery that is charged at under 20% DoD can last many times longer than these numbers due to the trickle charge that occurs with most devices.  

On the other side of the fence are the so called “quick chargers.”  While they are great in a pinch, they VASTLY decrease the life of a lithium battery because of the much, much higher heat and current they produce.

If that wasn’t enough to overheat your brain, then consider that 100% is relative.  In fact, every single day that your battery exists 100% is less than the day before.  Unlike a standard AA battery that seems to stop working all at once, a lithium seems to shrink with use.  A full glass on day one is a full thimble at the end of its life.  Regardless, you will see 100% when it is fully charged, because it is 100% of that moment’s capacity, not 100% of the battery…  But, I digress….

So… What does all this mean?

  1.  Stop worrying about charging devices before first use if they have a lithium battery.
  2. Use a new device until it is at 0% then charge it all the way… or as much as you can… Basically, use it that day and maybe the next, then plug it in overnight.
  3. Stop worrying about your battery “memory”.  It doesn’t exist.  Do a single discharge-recharge cycle if you think it might help.
  4. Stop using “quick” chargers.
  5. Stop using your battery to 0% every day, if you can help it.
  6. Stop worrying about charging “too long.”
  7. Stop worrying about charging “too often.”
  8. Stop leaving your phone in hot places.
Actually…  Just stop worrying about your phone battery.  Common batteries are designed to last about 3 years under typical usage.  Stop overthinking it.  Stop being typical, don’t get it hot, and it will last longer. Me

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