Six tips for getting the most from your rechargeable batteries

Six tips for getting the best possible life out of the Li-Ion rechargeable batteries inside your smartphone, tablet or notebook.
Written by Adrian Kingsley-Hughes, Senior Contributing Editor

I'm surrounded by devices that owe their lifeblood to Li-Ion rechargeable batteries. And as most devices are now built in such a way that it makes replacing the battery tricky - not to mention expensive - you want to get the best possible lifespan out of that battery.

How much of a difference can taking care of the battery actually make? In my experience, a lot. I have both a second-generation iPod nano that I bought around December 2006, and a first-generation iPod touch I picked up in 2008 that are both still going strong on the original battery.

So, how do you get the most out of Li-Ion rechargeable batteries?

1: Understand the "recharge cycle"

Every battery has a finite lifespan, and this is given as the "recharge cycle" or "battery cycle." Put simply, this is the number of charge/discharge cycles that a battery is expected to endure before it is no longer fit for service. Some hardware manufacturers publish this figure while others do not. For example, Apple makes this information available, stating that the iPhone battery is designed to retain up to 80 percent of its original capacity at 500 full charge and discharge cycles, while the MacBook Pro or MacBook Air is designed to deliver up to 1000 full charge and discharge cycles before it reaches 80 percent of its original capacity.

Some people think that they can dodge this charge and discharge by topping up their battery regularly so the battery doesn't get fully discharged. Unfortunately, as Star Trek's Mr Scott was fond of saying, "you cannae change the laws of physics." If you only let you battery discharge by 25 percent, then doing this four times counts as a cycle. Same if you do five charges after 20 percent discharge, or even 20 recharges after 5 percent discharge.

What you can do though is prevent unnecessary cycles by keeping devices plugged in and charging where possible. However, be smart about this, only leave things plugged in when they are in use, and don't leave them on charge all the time as this can cause heat to build up, which itself will damage the battery.

In other words, don't put the battery through unnecessary cycles. Understand that I'm not saying keep the device on charge all the time - that would also be bad for the battery because it needs a regular workout to keep its internal chemistry in good condition - just be aware of wasting cycles.

2: Full discharge vs. Partial discharge

Some people say that you shouldn't allow a Li-Ion battery to become fully exhausted before recharging, other people say it doesn't matter.

Truth is, with modern Li-Ion batteries it doesn't really matter because their discharge is closely regulated by on-board circuitry.

This used to be an issue with the old NiCd batteries because they could discharge to such a point where they would become impossible to recharge (those batteries also didn't like being charged too often and were much more sensitive to temperature). The same goes for lead-acid batteries, which also don't take too well to being discharged too much unless they are rated for "deep cycle."

3: Use the right charger

I'm a big believer in using the right charger for the right device.

It might be more convenient to pack one charger and a bunch of cables for trips, but for long-term usage you're better off using a charger designed for your device because that's delivering the right amount of power for the battery. Regularly using a charger that delivers too much or too little power will ultimately affect the longevity of the battery.

If you are going to go down the third-party charger road, then make sure they are a reputable brand. No-name junk might look and feel like an original charger, but based on testing I've carried out I've found that what comes out of the cable can vary wildly. I've also seen cheap chargers pour our masses of acrid smoke, and even blow up while plugged in. There's aren't the sort of dramas I like to see happening at home or in the office.

Does it really make sense to hook up a $500 tablet to a $2 charger? I think not. While battery protection circuits built into devices do a good job of shutting off power that could damage a battery, poor quality chargers can still do a lot of damage.

4: Keep an eye on the temperature

Room temperature - around 20°C/70°F - is the best temperature to charge equipment at. However, since we don't all life in climate-controlled rooms, we can extend this range out to 5 to 45°C/41 to 113°F. Anything either side of this and things can get bad for the battery. This is especially true for charging the battery at temperatures below 0°C/32°F, which can permanently damage the battery.

Subjecting Li-Ion batteries to temperature extremes can also physically damage the battery, causing it to warp or crack. This, in turn, can damage the device containing the battery.

5: Avoid physical stress

Drops and falls can damage batteries, causing it to leak a cocktail of corrosive chemicals, all of which are bad for electronics, not to mention your skin should you happen to get any on you.

6: Long-term storage

What should you do if you plan on storing your device for an extended period? The normal instinct is to fully charge the device, but I've found that only charging it up partially - around 50 percent - is the best way. Storing a battery in the discharged state can push it to the point where it won't recharge, and storing a battery fully charged can shorten its life.

Long-term storage is best done as close to room temperature as possible. So avoid really cold rooms or keeping the device next to a radiator.

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