Lithium-ion Longevity: Prolong your battery’s life

Preface

I remember my first laptop pretty distinctly. I got it for Christmas/birthday roughly 9 years ago. I remember it mostly because it was a the perfect example of a hardware design disaster. It suffered from “heat exhaustion” so badly I shipped it to the manufacture 3 times and each time they found nothing wrong with it. Of course every time I called tech support, they had me take out the RAM and the harddrive and put them back in and make sure the BIOS was up-to-date. Then, finally, I got them to replace the motherboard and I think even the entire computer replaced again later. But to no avail, the new hardware had the same problem. A total catastrophe in heat management. Thank goodness they discontinued its production within a few months I think.

However, more to the point of my story, I also remember this was the first time I learned about how to get the most life out of a rechargeable battery. I can’t tell you what kind of battery it was, I just distinctly remember being told to charge the battery 100% and then run the computer until it died at 0%.

Since that day, I’ve tried to do the same thing for most of my rechargeable electronics. However, more recently, I’ve kinda started to give up on the idea. I never did it with my iPad 2 nor my iPhone 4 either (I think). I started getting this feeling it did nothing for my battery.

I recently discussed the whole “charge-and-kill” concept with two friends, one of which just bought a new iPad 2 and another an electrical engineer. The one who bought the iPad 2 was talking about how he hadn’t charged his device for a couple days and didn’t plan to until the battery died to increase its longevity. I told him I didn’t really think that did much to modern batteries. I told him what my uncle (also an electrical engineer) told me, that it really only applied to “old” batteries and that the new ones didn’t need to be fully discharged during the first use. The electrical engineer immediately chimed in that it still applied to Lithium-ion (Li-ion) batteries and gave me his reasons. I didn’t argue with him because I wasn’t sure. Afterall, I’m only a systems guy, not a hardware guru.

After that discussion, I decided to do some research and get the facts on extending battery life in our modern electronics. Along the way I’ve encountered more people who fully discharge their devices in hopes of prolonging battery cycle life. I hope this post will be of use to all who adhere to this dated philosophy.

NiCd: Debunking the Modern Myth

First, let’s talk about what I’ve dubbed the “charge-and-kill” myth. Where did this concept originate and is it really a myth?

Older rechargeable electronics typically run on Nickel-Cadmium (NiCd) batteries. These batteries require a process Battery University refers to as priming. Priming is…:

…a conditioning cycle that is applied as a service tool to improve battery performance during usage or after prolonged storage. Priming relates mainly to nickel-based batteries….Manufacturers advise to trickle charge a nickel-based battery for 16 to 24 hours when new and after a long storage. This allows the cells to adjust to each other and bring them to an equal charge level. A slow charge also helps to redistribute the electrolyte to eliminate dry spots on the separator that might have developed by gravitation.

Battery University also discusses the process of formatting. Some batteries, like NiCd and lead acid-based batteries, are formatted through continued use. Formatting…:

completes the manufacturing process and occurs naturally during early usage when the battery is being cycled….Nickel-based batteries are not always fully formatted when they leave the factory. Applying several charge/discharge cycles through normal use or with a battery analyzer completes the formatting process.

Furthermore, NiCd batteries are known to develop a kind of “charge memory” over time. In other words, if you never fully charge and discharge the battery, it will only remember the basic range of charge it holds. For example, if you always keep your battery charged between 50-100%, it will start to remember this charge range and lose its ability to hold the original 0-100% range. This memory effect occurs from a lack of use of the materials in the battery, which actually begin to lose their battery-like, charge holding characteristics.

This is why so many people talk about completing a full charge/discharge cycle with electronics. Thus the “charge-and-kill” method applies to NiCd batteries; however, it does NOT apply to Li-ion batteries.

The Truth About Li-ion Batteries

Li-ion batteries do NOT suffer from the memory effect mentioned above. Li-ion batteries do not require priming or formatting. To quote Battery University again:

Lithium-ion is a very clean system and does not need formatting when new, nor does it require the level of maintenance that nickel-based batteries do. The first charge is no different than the fifth or the 50th. Formatting makes little difference because the maximum capacity is available right from the beginning.

Battery Univeristy goes on to describe what some people attribute to a pseudo-memory effect being corrected in a Li-ion:

Nor does a full discharge improve the capacity once faded. In most cases, a low capacity signals the end of life. A discharge/charge may be beneficial for calibrating a “smart” battery, but this service only addresses the digital part of the pack and does nothing to improve the electrochemical battery. Instructions to charge a new battery for eight hours are seen as “old school” from the nickel battery days.

Which begs the question: How do you prolong the life of your Li-ion battery?

Five Ways to Prolong Li-ion Battery Life

I will discuss 5 of the best ways to get the most out of your Li-ion rechargeable battery. Battery University has an extensive article on the why’s.

  1. AVOID HEAT. Heat is bad new bears for just about all electronics. It’s also true for your battery; keep it cool. For laptops, avoid surfaces that will inhibit cooling or block fans (e.g. blankets, pillows and all sorts of fluffy, soft things). Even better, use a laptop stand. Lifehacker has a lot of cool, cheap ($8) DIY laptop stands. If you are super cautious, use a cooling pad. If your phone is really toasty, read this.
  2. UNPLUG WHEN FULLY CHARGED. Don’t keep your device plugged in perpetually after it has reached a full charge. If you want to leave it plugged in overnight, get something like a Belkin Conserve Socket.
  3. DISCHARGE MODERATELY. Don’t discharge your battery to a shallow 90% all the time and then plug it in again. Conversely, don’t discharge your battery to a deep 0% or 10% routinely. Just keep it moderate around 50% or so. This yields an optimal cycles-to-usage ratio (see Battery University for a table).
  4. OBEY THE 40-80% RULE. Charging above 80% produces excess of heat. Charging longer (because you let your battery level drop so low) produces more heat.
  5. DEEP DISCHARGE ONCE A MONTH (OR SO). While this will not prolong the life of your Li-ion battery, it will keep the battery “smart.” In other words, it will more accurately report how much life is remaining.

Update: 1/16/2014

Based on user comment below, I have re-read the Battery University article referenced and have reevaluated some of my recommendations above. Instead of changing my recommendations or re-wording them, I would like to quote some of the more important lines from the Battery University article and you can make your own inferences.

  • “…the worst situation is keeping a fully charged battery at elevated temperatures…”
  • “A partial discharge reduces stress and prolongs battery life. Elevated temperature and high currents also affect cycle life.”
  • “Higher charge voltages boost capacity but lowers cycle life and compromises safety.”
  • “For long-term storage, manufacturers recommend a 40 percent charge. This allows for some self-discharge while still retaining sufficient charge to keep the protection circuit active.”
  • “Batteries are also exposed to elevated temperature when charging on wireless chargers. The energy transfer from a charging mat to a portable device is 70 to 80 percent and the remaining 20 to 30 percent is lost mostly in heat that is transferred to the battery through the mat.”
  • ‘Should I disconnect my laptop from the power grid when not in use?’ many ask. Under normal circumstances this should not be necessary because once the lithium-ion battery is full the charger discontinues charge and only engages when the battery voltage drops. Most users do not remove the AC power and I like to believe that this practice is safe.”

My apologies for any misinformation and my thanks to the comments.