How to extend the life of your batteries

Here are a few things you can do to make your lithium-ion (Li-ion) batteries last longer and maximize running time, so they don’t need to be replaced as often, whether they be used in an electric car, a large home installation or in your portable device, such as a smartphone or laptop.

Tip 1: Use it but avoid full discharges

It is important to remember that batteries degrade not only during use, but also when sitting idly on a shelf. This is one reason why most manufacturers specify not only a cycle life but also a calendar life for their batteries. Although a battery should deliver 100 percent capacity during the first year of service, it is common to see lower than specified capacities, and shelf life may contribute to this loss.

table 1.PNG

Table 1: Capacity drop as part of cycling. Eleven new Li-ion were tested on a Cadex C7400 battery analyzer. All packs started at a capacity of 88–94% and decreased to 73–84% after 250 full discharge cycles. The 1500mAh pouch packs are used in mobile phones.

Courtesy of Cadex

Similar to a mechanical device that wears out faster with heavy use, the depth of discharge (DoD) determines the cycle count of the battery. The smaller the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses. Partial discharge on Li-ion is fine. There is no memory and the battery does not need periodic full discharge cycles to prolong life.
table 2

Table 2: Cycle life as a function of depth of discharge. A partial discharge reduces stress and prolongs battery life, so does a partial charge. Elevated temperature and high currents also affect cycle life.

Note: 100% DoD is a full cycle; 10% is very brief. Cycling in mid-state-of-charge would have best longevity.

 

Steer clear of anything with questionable origin. And avoid buying something that you only expect to use a long time from now.

Tip 2: Keep it cool

Heat is the enemy of electronics. It can sap life out of each battery charge, and also shorten the battery’s overall lifespan. Li-ion batteries are typically happiest at around room temperature of 20 to 25°C.

In warmer temperatures, a protective layer inside the batteries breaks and needs to be reconstituted, which sucks up some of the energy capacity the battery has to offer.

And in colder temperatures the chemical reactions inside the battery slow down. When coupled with significant power draw, this causes a problem similar to roadworks during rush hour traffic: too many cars trying to get through too few roads.

On the whole, though, cold is usually less harmful than heat. So if you have the choice between placing your phone in the sun or the shade, the latter is probably preferable.

Tip 3: Avoid overcharging

The third tip relates to when and by how much batteries should be charged. One of the more widely known aspects about battery life is the “memory effect”.

In older rechargeable battery chemistries, such as nickel cadmium, partial charging and discharging significantly decreases the energy capacity.

What is less known is that the memory effect in lithium-ion batteries, if it exists, tends to be very small. Instead, they have quite nuanced characteristics. When not in use, batteries degrade most when fully charged. So if left for several days or weeks without use, they should ideally be kept at a relatively low charging state, e.g around 20% charged.

Conversely, when being charged and discharged a lot, it is best to keep the batteries as close to the 50% mark as possible. So if you are only charging and discharging batteries a bit at a time, it is much better to do this between 45-55% than between 90-100%.

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Want to keep your phone battery in shape? Never charge it to 100%

 

 

Tip 4: 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 5: Follow correct charging methods

Charging and discharging batteries is a chemical reaction, but Li-ion is claimed to be the exception. Battery scientists talk about energies flowing in and out of the battery as part of ion movement between anode and cathode.

The Li ion charger is a voltage-limiting device that has similarities to the lead acid system. The differences with Li-ion lie in a higher voltage per cell, tighter voltage tolerances and the absence of trickle or float charge at full charge. While lead acid offers some flexibility in terms of voltage cut off, manufacturers of Li-ion cells are very strict on the correct setting because Li-ion cannot accept overcharge. The so-called miracle charger that promises to prolong battery life and gain extra capacity with pulses and other gimmicks does not exist. Li-ion is a “clean” system and only takes what it can absorb.

For short-term battery emergencies

The above looks at preserving your battery life over the long-term. Conversely, if you’re looking to maximize the capacity of your battery today without worrying about tomorrow, here are a couple of tips.

Firstly and most importantly, reduce the load: close apps, turn off Wi-Fi and GPS, lower screen brightness, etc.

And secondly, keep your device in a warm (but not hot) place. A warmer battery allows the chemical reactions to take place more easily, thereby unlocking a little bit of extra energy.

Note that if the battery gets too hot then the device will ramp up its cooling system (if it has one), using power you want to preserve. And if it gets way too hot, it will shut down entirely for safety reasons. Depending on the application, typically Li-ion cooling systems kick in between 30-50°C, and shut down around 55-65°C.

However, as discussed above, keeping your device at an elevated temperature over a significant period of time will decrease its life substantially. And when your current battery not longer cuts it and you buy a replacement, you may want to consider following the four tips above.

Final disclaimers

Li-ion is not a single chemistry, but a range of chemistry. Lithium-ion batteries are a huge improvement over previous types of batteries. Getting 500 charge/discharge cycles from a lithium-ion battery is not unheard of. The above is intended as rough guide for iron-phosphate or cobalt-based cathode chemistry, which tend to be the most widely used. However, there are others including manganese-spinel which have slightly different characteristics. If in any doubt, ask the battery manufacturer for guidance.

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