How to charge lithium ion batteries
Whether smartphone, e-bike, cordless lawnmower, electric car or power tool: At some point, the battery will run out and the lithium-ion-battery will need to be recharged. As a specialist in the safe storage, transportation and disposal of rechargeable batteries, we explain how to charge lithium-ion batteries correctly. The good news: Compared to older nickel-cadmium batteries or nickel-metal hydride batteries, charging modern lithium-ion batteries or lithium-polymer batteries has become much easier. A memory effect, which can render the battery unusable after just a few charging cycles, practically no longer occurs with lithium-ion batteries. If you take a little care, overcharging or deep discharging are also unlikely. However, in order to maintain a high usable capacity even after many charging cycles, a few points should be observed:
Ideal charging conditions
You should always charge your lithium-ion batteries in accordance with the instructions in the user manual. Pay particular attention to the following points:
Only use chargers designed for the battery. These not only supply the correct voltage and the appropriate current for each point of the charging curve, but usually also have the necessary electronics for safe battery management.
Ensure the correct temperature. Every battery has a slightly different temperature range in which it can be charged safely. However, you cannot go wrong with ‘room temperature’. The temperature recommendation applies not only to the surroundings, but above all to the battery itself. So let it cool down or warm up before charging.
As with other electrical devices, rechargeable batteries should only be charged in dry and, if possible, clean environments. For batteries that are brought in from the cold and then charged at room temperature, attention should also be paid to condensation.
Due to the latent risk of fire, lithium-ion batteries should be charged on a fireproof surface or preferably in a fireproof charging box. Damaged lithium-ion batteries must not be charged at all and must be disposed of properly. ‘Properly’ means in particular that they must not be thrown into the normal waste bin but must be handed in at a collection point.
No memory effect with lithium-ion batteries
With old nickel-cadmium batteries (NiCd) or nickel-metal hydride batteries (NiMH), a memory effect often occurred: Without complete discharge before charging, the usable capacity was reduced in the long term. Good planning was therefore required for recharging the batteries.
Modern lithium-ion batteries or lithium-polymer batteries (LiPos) have no significant memory effect. The battery can therefore be charged even if it is not yet empty. As lithium-ion batteries do not need to be fully charged, intermediate charging is also possible, for example if the battery is not needed during a break.
Overcharging batteries and fully charging them
If the correct charger is used, modern lithium-ion batteries cannot be overcharged. The battery management system, which is built into the charger, the device supplied by the battery (e.g. mobile phone) or the battery itself, prevents the battery from being overcharged. This means that lithium-ion-batteries can normally be charged overnight without any problems. In the case of DIY charging solutions (which we strongly advise against), care must be taken to ensure that the power supply is cut when the final charging voltage is reached. Otherwise irreversible damage to the cells may occur, including explosion.
For some models, it is recommended that they are not or not always fully charged, but only up to 80 % of their capacity, for example. In addition, full charging is not recommended if the battery is to be stored for a longer period of time. The reason for this in both cases is that a fully charged battery has a particularly high cell voltage, which can cause the battery to age more quickly.
Revitalising deeply discharged batteries
Batteries can be used until they reach the so-called cutoff voltage. If a current continues to flow after this point, a so-called deep discharge can occur. As rechargeable batteries themselves always lose some current and devices in which they are installed normally also draw current, rechargeable batteries should never be stored with a low charge. They should also be removed from stored devices or at least disconnected.
Deep discharging can cause irreparable damage to the cells. For example, the membrane that separates the cathode from the anode may be damaged. The resulting short circuit can lead to so-called ‘thermal runaway’ when recharging. This causes the battery to burn out, emitting hot gases.
Consequently, it is not a good idea to revitalise a deeply discharged battery. Deeply discharged lithium-ion batteries pose a major hazard and must be disposed of safely and properly.
A distinction must be made between batteries that are actually deeply discharged and those where the internal battery management system has disconnected the cells from the terminals as a precaution when the final discharge voltage is reached in order to prevent deep discharge. There is then no longer any voltage between the terminals. Many chargers then either no longer recognise the battery at all or they interpret the missing voltage as a deep discharge. The effect in both cases is that the battery is not charged. Such a battery can generally be revitalised, but this should be left to people who know what they are doing – and who can check on the battery cells before they do so.
How to charge lithium ion batteries without charger
Sometimes, people who have lost or damaged their charger or cable wonder how to charge lithium ion batteries without a charger. The short answer is:
DON’T charge your batteries without a fitting charger!
Even if you have a fitting power source, battery management is difficult: Chargers have sensors and electronics to charge batteries with the right voltage and the right current and stop at cutoff voltage. Even if you have the necessary variables for your batteries available, managing these parameters by hand is tricky.
