Lithium Ion Batteries explained

Too many people I’ve met have misconceptions, wrong understanding or simply no idea at all about how to maintain the batteries inside their new spanking new electronic gadgets. More often than not, it will be one of those nifty, super-slim lithium-ion variants. So, after busting 4 myths about battery life, I’ll try to gather as many tips about Lithium-Ion batteries.

Tip 1: Lithium ion batteries are limited by their life-spans
Found an e-bay offer for a lithium-ion battery pack for your ageing notebook or PDA at bargain prices? Or saw that battery pack for your gadget in its dusty sealed package at the corner store of the flea market? Before you jump and snap it up, be sure to first check the manufacturer date.

We all know that all batteries are limited by a finite number of charging “cycles”. However, it is a little publicized fact that the lifespan of lithium-ion batteries are also limited by their manufacture date.

The fact is, your lithium-ion battery starts dying the moment it leaves the factory! Of course, the actual life-span of an unused lithium-ion battery can vary by a fair amount based on its internal charge as well as the external temperature. But suffice to say that you can expect to irreversibly lose 20% of a lithium-ion battery’s charge every year from its original date of manufacture.

PDA came with more than one spare battery? Take it out of its shrink-wrap and use it interchangeably – today. Thinking of buying a “spare” battery for use in future? Well, just save the money and buy it only when you are ready to use it.

Tip 2: Avoid allowing your device to discharge completely
Every wondered why your phone, Laptop or iPad is able to cheerfully tell you that “Your battery is now exhausted” for several seconds on its brightly-lid LCD screen before switching off? The reason is simple; there is an artificial circuit that shuts off the device when the charge in the battery is too low.

This extraneous circuit is built to protect from the damage that could result if the charge of your lithium ion battery falls too low. If you still don’t get it: if the charge of your lithium ion battery falls too low, the battery can get irreversibly and permanently damaged. So since Lithium Ion has no “memory effect”, it is better to simply charge your portable device as and when you can or remember.

To set your mind at ease, a “charge cycle” means a single iteration of depleting followed by a re-charge until 100% of battery charge. If you consume 50% of your iPod’s battery on day 1, recharge to 100% at night, and do the same thing on day 2, then you would have just finished up one charge cycle of its battery life.

Hence constantly recharging a lithium ion battery does not shorten the battery life more than normal usage would. Avoid letting it sit on empty for too long; instead, keep it charged-up if you can.

Tip 3: Take the battery out of your notebook computer when connected to AC helps… not!
Well ok, actually, taking out the battery from your notebook computer might help, but the reason it does is not really what you think it is.
It is not because of over-charging as most people might believe. There are some really smart circuits monitoring your lithium ion battery (See reason #2 above), and these circuits also ensure that your precious lithium ion never gets overcharged. So leaving the battery in when the AC is on has no detrimental effect whatever on the health of the battery.

However, if there is another killer of lithium ion batteries other than old-age, then it would be heat. Long term exposure of a lithium ion battery to temperatures higher than 40 degrees Celsius permanently reduces its total charge capacity by noticeable percentages chunks per year. Having said that, I would hazard that modern processor like the Centrino Duo runs quite coolly overall.

On the other hand, it is really painful to see someone plug their AC adapter to their laptop, carefully remove the battery and put it aside, then finally sit down and switch on their laptop. Then have someone trip over their AC adapter an hour into an unsaved document.

Tip 4: Don’t leave the battery at high voltage unused
Some also claimed that we should minimize the duration of the battery remain at high voltage (e.g. 4.2v / 100%). This is spoil the battery because the corrosion activities are relatively high when the battery is in high voltage/ full charge.
Put it short, after fully charge your battery, please use it ASAP. It won’t give birth little baby battery if you leave it there with full charge 

Tip 5: One way of Storing Battery for Long time
If you were to store your battery for a long time, discharge it to 40%. Keep it in a dry and cool place.
Putting the battery into the industrial grade vacuum bag and vacuum it (almost no air in the package), then store it in the refrigerator (around 0 -3 Celsius) should do the trick. Do this if i want to keep the battery there to sit a few months. Just don’t put it in a freezer Open-mouthed smile

Tip 6: Keep your batteries at room temperature

That means between 20 and 25 degrees C. The worst thing that can happen to a lithium-ion battery is to have a full charge and be subjected to elevated temperatures. So don’t leave or charge your mobile device’s battery in your car if it’s hot out. Heat is by far the largest factor when it comes to reducing lithium-ion battery life.

Tip 7: Think about getting a high-capacity lithium-ion battery, rather than carrying a spare

Batteries deteriorate over time, whether they’re being used or not. So a spare battery won’t last much longer than the one in use. It’s important to remember the aging characteristic when purchasing batteries. Make sure to ask for ones with the most recent manufacturing date.

Tip 8: Allow partial discharges and avoid full ones (usually)

Unlike NiCad batteries, lithium-ion batteries do not have a charge memory. That means deep-discharge cycles are not required. In fact, it’s better for the battery to use partial-discharge cycles.

There is one exception. Battery experts suggest that after 30 charges, you should allow lithium-ion batteries to almost completely discharge. Continuous partial discharges create a condition called digital memory, decreasing the accuracy of the device’s power gauge. So let the battery discharge to the cut-off point and then recharge. The power gauge will be recalibrated.

Tip 9: Avoid completely discharging lithium-ion batteries

If a lithium-ion battery is discharged below 2.5 volts per cell, a safety circuit built into the battery opens and the battery appears to be dead. The original charger will be of no use. Only battery analyzers with the boost function have a chance of recharging the battery.

Also, for safety reasons, do not recharge deeply discharged lithium-ion batteries if they have been stored in that condition for several months.

Here’s a little table that will compare the number of discharge/charge cycles a battery can deliver at various DoD(Depth of Discharge) levels before lithium-ion is worn out. We assume end of life when the battery capacity drops to 70 percent. This is an arbitrary threshold that is application based.

Depth of discharge

Discharge cycles

100% DoD


50% DoD


25% DoD


10% DoD


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

Specifying battery life by the number of discharge cycles is not complete by itself; equally if not more important are temperature conditions and charging voltages. Lithium-ion suffers stress when exposed to heat and kept at a high charge voltage.


Another table, referring to the 5th Tip, illustrates capacity loss as a function of temperature and state-of-charge. One can clearly see a performance drop of recoverable capacity caused by environmental conditions and not cycling.

Battery Temperature

Permanent capacity loss when
stored at 40% state-of-charge
(recommended storage charge level)

Permanent capacity loss when
stored at 100% state-of-charge
(typical user charge level)


2% loss in 1 year; 98% remaining

6% loss in 1 year; 94% remaining


4% loss in 1 year; 96% remaining

20% loss in 1 year; 80% remaining


15% loss in 1 year; 85% remaining

35% loss in 1 year; 65% remaining


25% loss in 1 year 75%; remaining

      40% loss in 3 months


Permanent capacity loss of lithium‑ion as a function of temperature and charge level. High charge levels and elevated temperatures hasten permanent capacity loss. Newer designs may show improved results.