How often should you charge lithium ion batteries?

Your product's battery life disappoints users. Complaints about capacity fading too quickly are hurting your brand. You need a charging strategy that preserves battery health for the long term.

The best practice is to perform frequent, partial charges. Avoid letting the battery completely drain. Start charging when it drops to around 20-30% and stop before it's completely full for optimal longevity and cycle life.

This advice might go against everything you've heard. For years, we were trained to fully discharge and then fully recharge batteries to avoid a "memory effect¹." But that applied to older Nickel-Cadmium batteries, not modern lithium-ion. As an engineer or product manager, giving your customers the right advice is crucial for their satisfaction and your product's reputation. I've spent my career helping clients understand these nuances. Let's get into the specifics so you can build a better product and a more informed user base.

What is the best charging routine for a lithium-ion battery?

Users are confused about charging. They ask if they should charge overnight or unplug at a certain percentage. Bad advice can prematurely degrade the battery, leading to customer complaints and warranty claims.

The ideal routine for a lithium-ion battery is "snacking." Charge it for short periods throughout the day instead of one long charge from empty to full. Keeping the state of charge between 20% and 80% maximizes its lifespan.

In my experience, the biggest factor in battery aging², after manufacturing quality, is how it's charged and discharged. Think of a battery like a mechanical spring. You can stretch it all the way out (0%) and compress it all the way down (100%), but doing that repeatedly will wear it out fast. Making smaller movements in the middle of its range causes much less stress.

Why Full and Empty States are Stressful

A lithium-ion battery is under the most chemical and mechanical stress at the extremes. When it's at 100% charge, the high voltage³ accelerates the breakdown of the electrolyte and cathode materials. When it's near 0%, discharging it too deeply can cause irreversible damage to the anode. This is why our custom battery solutions always include a Protection Circuit Module (PCM) to prevent over-discharge, but avoiding that state in the first place is even better.

A Practical Charging Strategy

Charging Method	Stress Level	Impact on Lifespan	Best For
Deep Cycle (0%-100%)	High	Shortest Lifespan	Not Recommended
Partial Cycle (20%-80%)	Low	Longest Lifespan	Daily Use
Full Charge (0%-100%)	Varies (High at top)	Shorter Lifespan	Occasional need for max runtime

For most products, from medical devices to consumer electronics, advising users to top up the battery whenever convenient is the best path to long-term performance.

Is it better to charge lithium-ion batteries to 80%?

You want to give users a simple rule. The "80% rule" is popular, but is it true? Following a myth could mean your product's runtime seems shorter than competitors' and frustrates users.

Yes, for extending the battery's lifespan, charging only to 80% is significantly better than charging to 100%. This practice dramatically reduces stress on the battery's chemistry, potentially doubling or tripling its total number of effective charge cycles.

The "80% Rule" isn't a myth; it's based on the fundamental chemistry of lithium-ion cells. I often explain this to my clients when we are designing the specifications for their products. The final 20% of the charge, from 80% to 100%, is the most difficult part for the battery.

The Science Behind the 80% Rule

To push those last ions into the graphite anode, the charger has to raise the voltage to its highest level. This high voltage, combined with the increased internal resistance as the battery fills up, generates more heat. Both high voltage and excess heat are the primary enemies of battery longevity. They speed up the chemical reactions that cause capacity to fade over time. By simply stopping the charge at 80%, you avoid the most damaging part of the cycle. This simple change can have a massive impact on the product's effective service life.

Practical Trade-Offs

Of course, sometimes your users will need 100% of the battery's capacity. The key is that charging to 100% should be done for immediate use, not for storage. For products that are extremely sensitive to lifespan, we can even design the Battery Management System (BMS) to automatically cap the maximum charge at a lower level like 85% or 90%, building longevity right into the hardware.

Is it better to keep lithium batteries fully charged?

Your product might be plugged in all the time, like a medical monitoring device or a point-of-sale terminal. You worry that this constant full charge is silently killing the battery inside.

No, it is not good to keep a lithium-ion battery fully charged. Storing a battery at a 100% state of charge, especially at warm temperatures, is one of the fastest ways to permanently degrade its capacity. The ideal storage charge is around 40-50%.

This is a critical point that many people miss. Leaving a device on the charger after it's full is worse than simply charging it to 100% and then unplugging it. Keeping the battery at that peak voltage is like holding that spring compressed for weeks or months on end—it loses its springiness.

High Voltage Stress and Storage

When a battery sits at 100%, the high voltage puts constant stress on its internal components, accelerating permanent capacity loss. Heat makes this problem much worse. A battery stored at 100% in a 40°C (104°F) room can lose over 35% of its total capacity in just a year. The same battery stored at 50% charge would lose only a few percent. This is why, at LithoTop, we ship all our batteries at a partial charge. I always advise clients that for long-term storage⁴ of their final products, they should follow a similar rule. We recommend a recharge every 3 to 6 months to keep the battery's voltage in a healthy range and combat natural self-discharge. This simple step preserves the battery so the end customer gets a product that performs like new.

Is it better to charge lithium batteries fast or slow?

Fast charging is a huge selling point. But you're concerned it's destroying the battery's long-term health, leading to unhappy customers a year down the line who complain that the battery doesn't last anymore.

Slower charging is almost always better for the long-term health and lifespan of a lithium-ion battery. Fast charging generates more heat and puts more physical stress on the battery's internal components, which accelerates capacity loss over time.

The desire for instant gratification has made fast charging a must-have feature for many devices. But as an engineer, you know there's no free lunch in physics. The convenience of a fast charge comes at the cost of the battery's lifespan.

The Impact of Heat and High Current

Fast charging works by pushing a high electrical current into the battery. This high current can cause the lithium ions to accumulate on the surface of the anode instead of neatly inserting themselves into it. This process, called lithium plating, is irreversible and permanently reduces the battery's capacity. It can also pose a safety risk in extreme cases. Furthermore, this high-current process generates significant heat, and as we've already discussed, heat is a primary driver of battery degradation.

Finding the Right Balance

The solution isn't to abandon fast charging, but to manage it intelligently. This is where a high-quality PCM or BMS is critical. For clients who need fast charging⁵, we recommend to integrate a temperature sensor (NTC) into the battery pack. This allows the charging system to monitor the battery's temperature and reduce the current if it gets too hot. A smart charger also uses a profile that charges fast when the battery is empty and automatically slows down as it approaches full, mitigating the worst of the damage.

Conclusion

For a long life, charge your lithium-ion batteries partially and often. Avoid the extremes of 0% and 100%, and charge slowly when you can. It's simple care.

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