For a while now, I have been providing certain advice on how best (and when) to charge your ‘portable’ devices (smartphones, tablets, laptops – and even your EV, though this last item is not so portable). So here goes; what you should and shouldn’t do, and why:
From Charging habits to maximize battery life by Robert Triggs July 24, 2019
Smartphone users — casual and enthusiast alike — are forever in search of longer battery life. While fast charging keeps us topped up every day, the absence of replaceable batteries means eventually the lithium-ion cells enclosed in our phones are going to age and deteriorate.
If you’ve held onto a phone for a year or more, you’ve probably noticed the battery doesn’t seem to last as long as it did when it was brand new. Two years down the line and many phones struggle to make it through the day on a single charge. Holding onto a phone past three years can even spell trouble for system stability.
Unfortunately, battery capacity inevitably declines with age. However, there are things you can do to prolong the life of your battery and handset. If you’ve ever wondered what the best way to charge your battery is, here are some scientifically proven tips for maximizing battery life.
Partial charging is the way to go
One particularly persistent battery myth is that you need to occasionally fully discharge and recharge to erase “battery memory.” This couldn’t be more wrong for lithium-ion batteries. It’s a leftover myth from lead-acid cells and it’s actually quite undesirable to charge your modern smartphone in this way.
Partial charging is just fine for lithium-ion batteries and can actually have some positive benefits for cell longevity. To understand why it’s important to appreciate how a battery charges. When closer to empty, Li-ion batteries draw constant current and operate at a lower voltage. This voltage gradually increases as the cell charges up, leveling off at around a 70 percent charge before the current begins to fall until the capacity is full.
Partial charging is just fine for lithium-ion batteries and even has some positive benefits.
Importantly, operating at a low voltage is good for a battery’s lifespan, increasing the number of available charging cycles before you’ll start to see a major reduction in capacity. Roughly speaking, every 0.1V decrease in cell voltage doubles the cycle life, according to Battery University. Therefore, charging up your phone in that 30 to 80 percent range keeps the voltage lower and prolongs the battery lifespan.
Lower battery voltages help prolong capacity over time. Green: lower voltage charging for first ~65%. Yellow: Start of constant voltage. Red: Long period of high voltage charging for last 15%.
Furthermore, the “depth-of-discharge” has a similar effect on the total discharge cycles before battery capacity drops off. This refers to the amount the battery used up in between charges. Smaller discharges, in the region of 60 percent rather than 100 percent between refueling can double the lifespan of your battery, and only using 20 percent can double the life again.
Small but regular top-ups are much better for Li-ion batteries than long full charge cycles.
Using up just 20 percent of your battery between charges isn’t going to be practical for most people, but topping up when you’ve used about half will see a notable improvement in your battery life over the long term, especially if you avoid charging up to full each time too. The bottom line is that small regular top-ups are much better for Li-ion batteries than long full charge cycles.
Docks are convenient but you shouldn’t leave a device in one once it has hit 100% charge.
Avoid idle charging
Charging overnight or in a cradle during the day is a very common habit, but it’s not recommended for several reasons (the old “overcharging” myth isn’t one of them). First, continuous trickle charging of a full battery can cause plating of the metallic lithium, which reduces stability in the long term and can lead to system-wide malfunctions and reboots. Secondly, it leaves the battery at the higher stress voltage when at 100 percent, as we just mentioned above. Third, it creates excess heat caused by wasted power dissipation.
Continuing to charge when a phone is at 100% is a recipe for voltage and temperature stress.
Ideally, a device should stop charging when it reaches 100 percent battery capacity, only turning the charging circuit back on to top up the battery every now and again — or at the very least reducing the charging current to very small amounts.
I tested a few phones charged to 100 percent and they continued to pull up to half an amp and sometimes more from the wall outlet. Turning the smartphones off doesn’t make a difference in many cases, with only the LG V30 dropping down to below 20mA when off and still plugged in. Most phones hover between 200 and 500 mA.At 100 percent charge, this phone still draws 200mA to keep the battery topped up.Using the phone increases the current draw, inducing a mini cycle in the battery.
A final point worth mentioning is parasitic load. This occurs when the battery is being drained significantly at the same time as being charged, such as watching a video or gaming while charging.
Parasitic loads are bad for batteries because they distort the charging cycle and can induce mini-cycles, where part of the battery continually cycles and deteriorates at a faster rate than the rest of the cell. Worse still, parasitic loads occurring when a device is fully charged also induce higher voltage stress and heat on the battery.
Gaming or watching videos while charging is bad because they distort charging cycles.
The best way to avoid parasitic loads it to turn your device off while charging. But it’s probably more realistic to keep the workload very light while the device is plugged in, leaving it to idle most of the time. Remember to unplug it once the battery is topped up enough.
Heat is the enemy of long battery life
Along with all of the above, temperature is an equally key contributor to battery longevity. Just like high voltages, high temperatures stress the battery and make it lose capacity far more quickly than when kept at lower temperatures.
A cell kept between 25 – 30 degrees Celsius (77 – 86 degrees Fahrenheit) should retain around 80 percent of its capacity after the first year even when cycling from empty to full charge. Battery capacity will be higher than this after a year if smaller periodic charging cycles are used. Raising the temperature to 40C (104F) sees this fall to just 65 percent capacity after the first year, and a 60C (140F) battery temperature will hit this marker in as little as three months.
The ideal temperature to maximise battery cycle life is between 20 and 50°C
A battery dwelling in a full state-of-charge exposed to a high temperature is the worst of all worlds and the number one thing to avoid when charging your phone. So no leaving your phone under your pillow to charge at night or plugged in on the dashboard of your car on a hot day.
Fast charging technologies are a contentious issue here, as the higher current and voltages can definitely lead to a hotter device while charging. Fast charging was never really envisioned for full-cycle charging though, instead, it’s a fast way to top up your phone quickly to get it back in your hands. Leaving your phone to quickly charge up for 15 to 20 minutes won’t lead to major overheating problems, but I certainly don’t recommend using them for overnight charging.
Bringing this all together
Broadly speaking, smaller regular charge cycles and keeping your phone cool are the key things to remember. Although I should point out that different phone batteries will always age slightly differently depending on how we treat them. Here’s a summary of the battery tips above:
What’s the best way to charge your smartphone?
- Avoid full cycle (zero-100 percent) and overnight charging. Instead, top-up your phone more regularly with partial charges.
- Ending a charge at 80 percent is better for the battery than topping all the way up to 100 percent.
- Use fast charging technologies sparingly and never overnight.
- Heat is the battery killer. Don’t cover your phone when charging and keep it out of hot places.
- Turn your phone off when charging, or at least don’t play games or watch videos to avoid mini-cycles.
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OK, so that’s all well and good for lithium-ion cells, but what about my electric toothbrush or my cordless power tool? It’s probably using Nickel-Cadmium (aka NiCad) batteries. So what are they and what kind of care and feeding do they need?
From What The Heck is a NiCd Battery?
If this is not your first stop in the NiCd information trail I am sure the information that you have read, heard, or found on the internet is just about overwhelming. In this tutorial we will do our best at keeping it simple, accurate, and to the point. If you have questions that are not addressed, please let us know and we hopefully be able to help.
What NiCad batteries are
‘NiCd’ is the chemical abbreviation for the composition of Nickel-Cadmium batteries, which are a type of secondary (rechargeable) batteries. Nickel-Cadmium batteries contain the chemicals Nickel (Ni) and Cadmium (Cd), in various forms and compositions. Typically the positive electrode is made of Nickel hydroxide (Ni (OH) 2) and the negative electrode is composed of Cadmium hydroxide (Cd (OH) 2), with the electrolyte itself being Potassium hydroxide (KOH).
How NiCd Batteries are Unique
NiCad batteries are different from typical alkaline batteries or lead-acid batteries in several key ways. One of the main key differences is in cell voltage. A typical alkaline or lead-acid battery has a cell voltage of approximately 2V, which then steadily drops off as it is depleted. NiCad batteries are unique in that they will maintain a steady voltage of 1.2v per cell up until it is almost completely depleted. This causes the NiCad batteries to have the ability to deliver full power output up until the end of its discharge cycle. So, while they have a lower voltage per cell, they have a more powerful delivery throughout the entirety of the application. Some manufacturers make up the voltage difference by adding an extra cell to the battery pack. This allows for the voltage to be the same as the traditional type batteries, while still retaining the constant voltage that is so unique of NiCads. Another reason the NiCad batteries can deliver such high power output, is they have very low internal resistance. Because their internal resistance is so low, they are capable of discharging a lot of power very quickly, as well as accepting a lot of power very quickly. Having such a low internal resistance keeps the internal temperature low as well, allowing for quick charge and discharge times. This feature, combined with the constant voltage of the cells, allows them to put out a high amount of amperage, at a consistently higher voltage than comparable alkaline batteries.
Power Tool Applications
One of the most practical applications for NiCad batteries is in cordless power tools. Power tools demand a high amount of power delivery throughout the entire time of use, and do not function as well with dropping voltages as a typical battery would deliver. With NiCad technology, power tools are able to operate at full capacity for the entire time of use, not only the first few minutes of operation. With a Lithium-ion, alkaline, or even a lead-acid battery, the power tool will perform extremely well from the start, with a steady decline in power, until the power tool barely works at all. NiCads, on the other hand, will cause the power tool to stay at full power up until the very end of the charge. Not only that, but then NiCads can be safely charged in as little as 1-2 hours!
Charging NiCd batteries
Another unique feature of NiCad batteries lies in the way they charge. Unlike a lead-acid battery which can take large variations in amperage and voltage while charging, the NiCad batteries require steady amperage and only very slight variations in voltage. The charge rate for a NiCad is right between 1.2 V and 1.45 V per cell. When charging NiCad batteries, a charge rate of c/10 (10% of capacity) is normally used, with the exceptions being speed chargers, which charge at either c/1 (100% capacity) or c/2 (50% capacity). NiCad’s have the ability to receive a much higher rate of charge up to 115% of their total capacity, with minimal reduction in life span, which makes NiCad batteries the ideal battery for power tools. If you notice the battery heating up while it is charging, cool it down, and then complete the charge. The chemical reaction in a NiCad while charging is heat absorbing, instead of heat producing, so higher power absorption is possible while charging, allowing for the quick recharge times.
Storing NiCd Batteries
When storing NiCad batteries, be sure to pick a cool, dry place. The temperature range for storing batteries is between −20 °C and 45 °C. When preparing to store NiCad batteries, be sure to discharge the batteries fairly deeply. The range in recommendations is between 40% and 0% charged when going into storage. NEVER short circuit a NiCad to drain as this causes excessive heat and can cause hydrogen gas to be released…AKA-Boom! The self-discharge rate for NiCad’s is right around 10% at 20 °C, and rising up to 20% at higher temperatures. It is recommended not to store NiCads for an extended amount of time without occasionally using the batteries. Over long periods of storage the cadmium in the NiCad can form dendrites (thin, conductive crystals), which can bridge the gap between contacts and short out the cell. Once this happens, there is really nothing that can be done to fix it long term. The best way to prevent this from happening is frequent use.
The Memory Effect
One of the most discussed topics about NiCad’s is whether or not they have a ‘memory’. The idea of a charge memory came when they started using NiCad batteries in satellites where they were typically charging for twelve hours out of twenty-four for several years.1 After several years it was noticed that the battery capacity has seemed to have declined severely, and while still operable, they would only discharge to the point that the charger would typically kick in, and then would drop off as if they were completely discharged. For the typical consumer this does not have a large effect, however, we do recommend fully discharging the NiCad you are using before recharging. Occasionally completely draining (but NEVER short circuiting) a NiCad can prevent the on setting of this mysterious battery ‘memory’. An effect with similar symptoms to the memory effect is what is called the voltage depression or lazy battery effect. This is caused by frequent overcharging of the NiCad. You can tell this is happening when the battery appears to be fully charged but discharges quickly after only a brief period use. This is not the memory effect, which is limited to NiCad batteries alone, but is something that can happen to any battery, and is almost always from overcharging. Occasionally this can be fixed by running the battery through a few very deep discharge cycles, but doing so can reduce the overall life of the battery. NiCad batteries are the only battery chemistry that benefit from completely discharging before recharging.
Proper Disposal
NiCad batteries contain Cadmium, a highly toxic ‘heavy’ metal. Never burn NiCads, and never throw them in the trash or break them open. Always recycle NiCad’s at an official NiCad recycle place. As long as NiCads are kept sealed, and never short circuited or severely over charged, NiCad batteries are perfectly safe to use, and do not vent toxic material. If a NiCad battery is treated well, it should last to the 1000 cycle mark. Speed charging NiCads can slightly shorten their life span, as can extended improper storage.
Summary
While limited in application, NiCad batteries are an exceptional choice for all of your cordless power tool requirements. There are other chemistry batteries coming online as technology marches on, however the best bang for your buck, insofar as Power Tool replacement batteries, still lies with this tried and tested battery type.
