This post includes input from my colleague Brad Willard, Manager, Product Safety & Test, Engineering Shared Services, Zebra. Brad serves on Zebra’s Green Product Council and is our battery safety expert.
If you’re plugging in your mobile computer, tablet or wearable whenever it’s convenient, or constantly topping off the battery to keep a full charge “just in case” you can’t charge it later, you’re killing your battery and draining your bank account.
That’s because a battery is only built to last a certain number of charge cycles.
Does that mean that if you’re plugging your device in three times a day, completing only partial charges each time, that your battery could die in approximately four months (~166 days) if it’s built for a 500-cycle lifespan?
Not necessarily, but your battery life could be cut in half. It all depends on your charging habits. So, let’s talk about what can either extend or shorten the life of your battery and device by asking and answering a few questions:
Q: Is every battery charging event considered a “charge cycle”? Or does the battery have to go to zero and then fully recharge for it to be considered a full cycle?
A cycle is defined as 100% of the battery’s capacity, but it does not have to be discharged in one go to be considered a “charge cycle.” Two days of using 50% capacity or four days of using 25% capacity are both equivalent to one full cycle. It doesn’t matter if you charge back to full each day between those 25-50% discharges or not.
Q: So, if I only discharge a battery 70% today (and have 30% remaining when I plug it in to recharge), that would be equivalent to using 70% of a cycle, right?
Correct. The battery would only be depleted a full cycle once the battery is discharged (or used) another 30%.
Q: If I only let the battery drop to 30% before recharging (because I don’t want to get stuck somewhere without a fully charged device), but I always charge to 100%, is that helping or hurting the battery’s health?
There are certain extreme charging behaviors/methods that will negatively impact battery health and deplete its usable life faster. For example, charging to a higher voltage/percentage (such as charging all the way to 100%), charging faster, or keeping the battery on the charger longer (trickle charging) can all harm the battery and shorten its lifespan.
That said, there are three variables in particular that contribute to battery swelling and capacity fade (the things that shorten battery life):
1, State of Charge
3. Time Duration
If any two of these variables are high, then the third needs to be low.
Therefore, it’s ok to charge a battery to 100% full *if* the temperature isn’t extreme and the amount of time the battery will be kept at 100% is less than a few weeks.
The two charging behaviors that I see which accelerate battery wear-out the most are:
1. Leaving the battery on continuous charge for months at a time. One real life example was a customer who purchased “spare” tablet computers and left them in the charging dock for several months. The best practice here would be to charge the device to 50% and then store it separately from the charging dock until you’re ready to actively use it.
2. Shallow discharge cycles of a battery where it is fully charged, the device is used for a short period of time, and then the device is put back in the charging dock. When the battery reaches its peak charge state, the degradation rate is the highest. This rate slows down as the battery voltage slowly decays down. Frequently topping off the battery causes the battery to spend more time in the peak charge state and thus accelerate degradation.
However, heat is not your battery’s friend either. So, keeping a battery cool, but not freezing, can help extend its life.
Q: Are the recommended battery charging practices applicable to all types of devices (i.e., tablets, wearables, headsets, scanners, RFID readers and mobile printers)? Or only handheld mobile computers (i.e., the ones that look like smartphones)?
Every type of device that uses lithium-ion cells (all of them!) will benefit from you employing the same best practices I described above – if you want to maximize battery endurance, which I’m sure you do since it’s good for the bottom line in so many ways. You can also download Zebra’s full Battery Best Practices guide here.
Q: If I have a fleet of shared devices that are used around the clock across multiple shifts by my team, how should I advise them to recharge the devices so that the battery can get through a full cycle without disrupting productivity?
If an employee’s battery has dropped below 50%, then they should charge their devices during their next break. Charging for 20 minutes should give the associate two hours of additional runtime.
Q: We keep additional batteries on hand for workers to swap out when their battery gets low, and they don’t have time to recharge. Is there a “best” time for that swap to occur, though? Could they wait until the battery is almost dead, or should they swap sooner?
For users that perform battery swaps, it is recommended to swap when the battery charge level drops to 20-30%.
Q: What about wireless charging? Is that potentially beneficial or harmful to devices with lithium-ion batteries?
There is some nuance to wireless charging. On the one hand, wireless charging will typically generate more heat than a wired charger. However, the amount of heat being created drops significantly once the battery finishes charging. So, gauging if wireless charging is helpful or harmful gets back to the three factors: the battery charge state, battery temperature, and time. If any two factors are high, then the third should be low.
I wouldn't recommend wireless charging in a hot environment like on a vehicle dashboard or next to a south-facing window. And by hot, meaning the surface of the device is 40˚ C or higher. This type of heating is a combination of air temperature, solar radiation, and heat generated either by the charging system or some other heat-producing equipment nearby, and it can be damaging to any type of device, even rugged ones.
To share a real-world example: a beverage company using a Zebra tablet computer and its team kept the charging dock on top of a bottling machine. In the summertime, the air temperature was 35˚ C and the heat from the bottling machine increased the tablet temperature to 45˚ C. They only took the tablet off the dock for about 15 minutes per eight-hour shift, so the battery charge state level was nearly 100% all the time. After about two months, the battery swelled so much that the tablet lost electrical contact with the charge dock. If they had used a wireless charger, the device temperature would have been a few degrees hotter and the swelling would have happened even sooner.
- Fast chargers are NOT better than traditional chargers in terms of extending overall battery life. In fact, fast chargers are worse. Slower charging is always better for battery health. Additionally, aftermarket battery chargers may prematurely degrade a battery's cycle life or shorten product run-time. So, it’s always recommended to use OEM charge accessories as they are designed to optimize both battery cycle life and run-time.
- Do NOT allow devices to deplete as much as possible before recharging. This is an outdated practice from an older chemistry of batteries (Nickel-Metal Hydride [NiMH]). High depths of discharge for Li-ion batteries will actively harm them. It is best to keep these batteries within moderate ranges of states of charge (20-80% or even 30-70%), though it is not the end of the world to charge to 100% or deplete to empty once in a while.
- Do not keep devices on the charger to “trickle charge” when they are full, if possible. If a battery is empty, charge it to at least 30% before using it, if not more.
With all this in mind, I imagine you’re going to want to take a close look at how you or your team is currently charging device batteries – and how you’re using your devices between charges. Are there adjustments that need to be made to improve device/battery efficiency?
You certainly don’t want to be replacing a battery – or entire device – very often, especially if you’re responsible for funding or managing a fleet of dozens, hundreds or thousands of devices for your employees.
Plus, something else to consider beyond the financial and operational costs of improper battery charging: the environmental cost.
Prolonging the life of your battery results in fewer batteries needed per mobile device/ terminal. This lowers the lifecycle environmental impact of the device by requiring less raw materials, less manufacturing, less transportation, and less waste disposal of batteries. Batteries contain valuable and impactful materials such as gold, cobalt, and lithium. Avoiding excess extraction can help the environment and your bottom line. Another environmental benefit of using charging practices that prolong your batteries’ lives is that these same practices tend to use less electricity and therefore produce fewer emissions.
IN OTHER WORDS
I realize how nerve wrecking it can be to worry that you’ll get stuck with a dead battery, which is why it’s important to understand these few simple changes you can make to your battery charging habits. Follow the advice provided above – and in this Battery Best Practices guide – and you’ll find your battery will last a lot longer than it probably has in the past (before you knew the right way to charge).
If you have more questions about anything I’ve shared or want to talk about a good change management approach for battery charging (to get your entire team in the habit of doing things right), feel free to reach out to me or your local Zebra representative.