Jehu's Charging Tips for Lithium Ion Batteries

Jehu's Charging Tips for Lithium Ion Batteries

Lithium-ion batteries require care to safely achieve the maximum battery life span. Battery charging is a key piece of knowledge that is required for making sure your lithium batteries last long, remain safe, and perform well. What do I need to know about charging lithium ion batteries?

Charging stored batteries
It's important to know that it is recommended to not leave batteries unused for extended periods of time, either in a product or in storage. Have a battery that has been unused for 6 months? Check the charge status and charge it. If you notice any corrosion, sweating/discoloration or chemical smells, dispose of the battery safely and appropriately.

Charge Cycles
The typical life of a lithium-ion battery is 300 to 500 charge cycles. One charge cycle is a period of use from fully charged, to fully discharged, and fully recharged again. Lithium-ion batteries have a limited life and will gradually lose their capacity to hold a charge. Lithium-ion batteries self-discharge when not in use or while in storage, so routinely check the battery’s SOC (state of charge).

Choosing a Charger
Chargers are designed according to the chemistry of the battery. For an accurate charging voltage, the correct type of charger is required.

You need to consider the charging voltage that is required. This depends on your cells. If your cells need to be charged to 4.2V per cell, this means you need a lithium ion charger with an output voltage: 4.2v x the number of cells (in series) in your battery.

Charging current must be considered, as some of the lithium-ion cells shouldn’t be set above 1C (meaning it can go from zero to 100% in 1 hour).

Keep an eye on the Battery Management System (BMS) if you have one. Some of them are rated for 5A charging, others less, others more.

Chargers have various power capabilities, so you need to consider if all you require is a low power charger / AC adpater, like our Xiaomi chargers, that is easily accessible, cheap, and low power. These usually operate with CC/CV (constant current/constant voltage), and usually have a rudimentary form of a trickle charge. Perhaps you need a Step-up / aluminum case charger, like this variable charger we like to use, which can be of better quality compared to plastic AC adapters, can tolerate high power levels, and have cooling fans. There are also programmable chargers, which tend to also be high quality and have multiple features for customizing charging profiles.

Charging and Discharging at the Extremes
Try to minimize the amount of time the battery spends at either 100% or 0% charge. Both extremely high and low “states of charge” stress batteries. BMSs (Battery Management Systems) will stop the charging once the device has reached 100% SOC, but many manufacturers caution against leaving batteries charging after they have completed charging.

Charging Past 100% SOC
Can lithium batteries charge past 100% SOC? Actually they can, but should you? If too much current is delivered to a battery, that could mean ripping out too many lithium ions, leading to degradation. Doing this requires pulling out crucial structural lithium ions, but good luck putting them back once you’ve messed up that internal structure. Not recommended.

What Charger Should I Use?
Not all chargers are created equal. Cheap chargers could have a damaging effect on your battery life, so it's best to stick with reputable brands, which is why we carry  Xiaomi chargers. Most good chargers have controls that limit current and stop it from charging when the battery is full, but some off-brand chargers might not have rigorous, or any, safety settings. This can lead to overcharging and battery damage. No bueno.

To choose a charger you'll need to know your application's voltage range. Is your system 16v, 36v, 96v? Lifepo4 or NMC chemistry? Slow-charge or Fast-charge (amperage)? Do you require protections (overcharge protection, etc)?

Types of Charge
If the charging level of a battery is low, it can get charged at a reduced constant current which is typically around 1/10, this is known as a Trickle Charge (also "pre-charge"). When the voltage of the battery increases, at a given threshold, the rate of charge is increased to its maximum capacity.

If the voltage is maintained at a high level at the initial stage or the battery has charged up to the maximum charge rate, this is regarded as a constant current charging stage (full rate charge) where the battery’s voltage rises slowly.

Discharging down to 0% SOC
Batteries are under the most strain when they're fully charged or completely discharged. The ideal SOC for a battery is 50% charge, meaning that half of the moveable lithium ions are in the lithium cobalt oxide layer and the other half are in the graphite layer. This equilibrium puts the least amount of strain on the battery, and extends the number of charge cycles it can withstand before degrading.

So if you want to keep your battery as long as possible, keep its charge between 20% and 80%. This way it spends as little time as possible with tons of lithium ions crammed into either layer, a situation which causes the layers to expand, physically straining them. The downside is that you’d only be getting about half as much charge every time you used it. It's a trade-off.

Should I Get a Fast-Charger?
Fast charging can be very convenient, as it can greatly speed up charging and drastically reduce the wait. The down side is that fast-charging puts more stress on the cells and can noticeably increase heat and decrease a battery's cycle life.

Lithium-ion battery care and maintenance can help you get the most out of your lithium battery projects, that's why it's a good idea to routinely check a battery’s charge status and to follow the manufacturer's charging recommendations whenever possible. This tip list is not meant to be exhaustive, but I hope it helps you on your DIY journey. Cheers!

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