Despite the fact that lithium-ion batteries have existed in commercial use since the 1990s, there’s still a lot of seemingly contradicting information on how to properly care for them. Some suggest that batteries should be completely discharged once in awhile. Others say you should avoid using your computer’s USB port to charge your devices.
For those truly concerned with the care of their lithium-based batteries, it’s important to discern myth from reality and understand what can harm your battery as well as how you can prolong its life. This is especially significant now, as many phone manufacturers are opting to make their devices with non-removable lithium-polymer batteries.
Understanding Li-Ion Batteries
To know what your battery’s needs and wants are, you first have to understand a couple of things about how it functions. Most Li-Ion batteries you’ll come across in electronics like smartphones will come in the form of lithium polymer (Li-Po) variants with lithium cobalt oxide (LiCoO2) as the cathode and graphite as the anode.
We’ll focus on this configuration as it’s the most popular. Other lithium-based batteries function pretty much the same. At 100% charge, the battery is at 4.2 volts and can discharge all the way down to 3.3 volts. At voltages above maximum charge voltage or below the minimum, the chemicals will experience excessive amounts of strain that may cause irreparable damage.
Fortunately, consumer-level hardware is built with this in mind. Your phone will stop charging when it reaches 4.2 volts and turn off before it ever reaches 3.3.
Because lithium-based cathodes have very predictable voltage patterns, it’s easy to measure how charged a particular battery is, as opposed to other rechargeable variants like NiMH and NiCd, which are still used in several commercial applications such as mouse/keyboard AA/AAA-type batteries.
Addressing the Memory Effect Myth
Many people believe that all rechargeable batteries have a “memory effect,” which goes something a little bit like this: if you never discharge a battery completely, it will form an “imprint” of its capacity at only the levels you discharged it to. Therefore, you should completely discharge your batteries once in awhile.
Although this is partially true for NiMH and NiCd batteries (which were basically the only commercially available rechargeable batteries during the 80s and early 90s), Li-Ion batteries found in most phones and portable electronics do not have this issue. It’s easier to think of it this way: NiMH and NiCd are chaotic and need to be brought to order once in awhile; Li-Ion follows strict rules.
In essence, you don’t have memory effect in lithium batteries that are commercially available. You don’t have to discharge them completely to continue to have accurate readings on battery level percentage. In fact, for some NiMH batteries, the same applies. Technology has advanced!
What Makes Lithium Batteries Happy
Lithium-ion batteries generally like to stay around 3.7 volts, which is about half their maximum capacity. So if you want your battery to be absolutely stable, you just have to keep it around 50% charge. Essentially, anything above that or below that introduces the battery to some levels of stress.
This information isn’t very useful in consumer electronics, though, since you’re not going to just sit around keeping your phone at 50% charge. Electronics are made with consumer use in mind. Again, your phone will shut off before it reaches 0% charge just to ensure that the battery isn’t drained all the way to its minimum charge tolerance (which is around 3.3 volts).
But even the 3.3-4.2 volt “safe area” is not the most stable for your battery. When a battery manufacturer lists how many charge cycles a battery can handle, it’s usually referring to 0-100% charges. However, just because your battery can tolerate hundreds of charge cycles from fully drained to fully charged doesn’t mean that you’re getting the most out of your battery.
To extend the lifetime of lithium-based batteries, you have to introduce it to the “lowest attainable level of stress.” Realistically, under most conditions, if you plan to use your device daily, keep the charge within 30% of its most stable state of 3.7 volts. To translate that into laymen’s terms, keep your battery between 20-80% charge. By not surpassing 80% charge, you don’t run the battery through a long trickle-charge process to try to fit as much electrical storage in it as possible. Once the electricity is “crammed in,” it takes more energy to continue the charge process, which exposes the chemicals to a minor amount of stress that degrades it over a significant amount of time.
After experimenting with this for years with various batteries of various capacities and compositions, I found that you can expect many more charge cycles (sometimes surpassing 50% more lifetime) before a battery degrades using this method. If you’re not that disciplined (as I’m often not either), simply not letting your battery level fall below 20% will have a meaningful impact in its longevity.
No matter how resistant your manufacturer says your battery is, it’s still a lithium-based piece of hardware, and this kind of chemistry tends to come under strain in a very predictable and universal manner. So if you have a battery that’s rated for 800 charge cycles, you might squeeze another 300-400 out of it following this rule. Remember, charge cycle ratings usually account for full discharge-recharge under normal conditions, accounting for the stresses that accumulators go through with these voltages.
For long term storage, there are different rules. If you plan to put a device into storage for more than a year, remember that lithium-based batteries love stability. Charge it up to (or drain it down to) 3.7 volts (that’s 50% charge) and keep it in some place cold or at room temperature. This ensures that the lithium cathode degrades as slowly as possible and provides the best possible experience once it’s taken out of storage.
Considering everything we’ve discussed, it’s time to compile it all into a set of commandments for maximum battery efficiency:
- Memory effect in lithium-ion batteries is a myth
- Keep your battery between 20-80% charge so it doesn’t stray too much from 3.7 volts
- Avoid exposing it to extremely hot temperatures
- For long-term storage, just drain or charge the battery so it’s at a 50% charge and keep it cool or at room temperature
Follow those four points, and you’re going to squeeze much more from your battery than the manufacturer’s rating. Although it takes a long time to explain why those rules exist, they’re essentially simple rules to follow!
If you have other tips or questions about how you should manage lithium-ion batteries, be sure to use the comments section below!