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HOW TO: Care For Your Battery

23 JUL
MacBook and iMac Mobile Phones (photo by Daniel Nanescu)

We’re well into the 21st Century, and while we don’t have flying cars or hoverboards (just yet) we do have a plethora of fantastical, battery-powered, hand-held devices. Laptops, phones, RC toys and the like are commonplace, but knowing which battery powers them and how best to care for it… not so much.

Be honest - you rarely think about your battery unless it isn’t working as expected, right? You’d be forgiven for thinking so, but batteries aren’t simply magic. They can, and should, be understood and cared for.

It’s all about reducing battery stress, in doing so your battery will last longer - not longer in-between charges, but have a longer lifespan. So let’s start by getting to know a little more about them:

Common Batteries

Li-ion Battery

Currently, the most common rechargeable battery for consumer products is lithium based. Typically lithium-ion (Li-ion) or lithium-ion-polymer (Li-poly). I'd bet when hoverboards do turn up they'd use Li-ions. Much of the battery lore that still exists today comes from older nickel based batteries - nickel-cadmium (NiCd) or nickel-metal-hydride (NiMH).

Memory Effect

phones

Nickel based batteries had, what was referred to as, a memory. Charging from anything above 0% might lead the battery to forget what 100% was. Eg: if charged from 50% the battery could remember 50% as 0% and cease operating once it got to 50% again. So it was best to charge Nickel based batteries from flat. Lithium batteries, however, do not have a memory.

Charge / Discharge Cycle

Battery

Batteries have a limited number full charge and full discharge cycles before their performance starts to deteriorate. They also discharge themselves when not in use. What counts as a full cycle varies between manufacturers, but typically letting power fall below 5% counts as a full discharge, and anything above 95% counts as a full charge.

Depth of Discharge (DoD)

Depth of Discharge

This is how far from a full charge your battery is when you decide to plug it in - i.e. if you charge your battery when it’s at 40%, your depth of discharge is 60%. The shallower the discharge depth (smaller percentage) the less stress you’ll put your battery under. This table shows how many times, on average, you can charge your battery from a certain depth before performance starts to deteriorate. Big difference if you let it run flat, right?

Ok, that’s a long way of saying you probably have a lithium battery. Also, what your parents told you about their nickel-cad batteries probably isn’t the best way to care for yours… so what is?

Battery Care

Initial Charge

Another relic of the nickel age, you don’t have to prime a lithium-ion battery (a.k.a fully charge it and then some). In fact, it may please you to know it’s best to use it for a little bit right out of the box. It’s even better not to charge it to 100% all the time, so don’t leave it charging overnight… ever!

Perform shallow discharges

Remember the table above? Lithium batteries are less stressed when charged from anything that isn't flat (100% DoD). Again, you don't even have to charge it to 100%. So if you have a spare 15mins - plug in!

Regular Charging

Aim to maintain a 40%-80% charge. Fast or high voltage chargers, while convenient, aren’t great to use all the time because (you guessed it) they can stress-out your battery. If you need power fast, reduce parasitic load by turning your device off. If you can’t, turn off as many features as possible (brightness, WiFi etc).

In this context - parasitic load is drawing power to charge and use your device at the same time, asking more of your charger and leaving your battery with less power to charge. To you and me, this means it takes longer... oh, and causes stress.

Keep cool

Increased heat = increased stress. Batteries perform more efficiently and last longer when kept as cool as possible. For Li-ions this is between 5°C and 45°C, which can be hard if other components (even charging) generate extra heat. Try to avoid direct sunlight or covering up any ventilation holes the device may have.

Re-Calibration (Full Discharge & Charge)

Does your phone tell you you've got 20% battery remaining one minute, then turn itself off the next? If so, your smart meter could be out-of-whack. Now - I know I’ve just told you a few times that fully charging a lithium battery can be bad, but hear me out.

The smart meter in lithium batteries calculates charge level and time remaining. After multiple shallow charges this meter can go a little funny, giving an inaccurate battery reading. Here’s how to recalibrate it:

  1. Charge the battery to full (from no less than 50% DoD)

  2. Fully discharge the battery (let the device run out / turn itself off)

  3. Charge at a wall socket with originally supplied charger

  4. Keep the device off while charging

A full charge cycle like this does increase stress, but in my experience the smart meter calibrates nicely on a single full charge and shouldn’t need to be done more than once a month (if ever). To keep a smart meter happy try to do this it at least once every 3 months.

 

Aerial view office deck Mobile Phones (photo by Daniel Nanescu)

Summary

So what have we learned?

Batteries live longer if you don’t stress them out too much. Keep your batteries healthy by:

  • Using the supplied / an original manufacturer charger

  • Aiming to maintain a 40%-80% charge

  • Not leaving it plugged in at 100%

  • Turning device or features off to charge faster

  • Only discharge from 100% to 0% if you need to recalibrate the smart meter

Keep these things in mind and your battery will last longer, but it isn’t designed to last forever. It will pack in after a few years no matter what you do - even if you just let it sit on a shelf. Speaking of which - if you’re going to store a battery for any length of time, it’ll be less stressed if you charge it between 25% and 50% first.

Ultimately though, these guidelines are just that: guidelines to keep your lithium battery healthy for as long as possible. If any of the above tips work for you, or you have your own, let me know in the comments below.

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Want more technical How Tos? Check out Si's other blogs: