One of the key issues with Li-ion batteries is correctly handling them in order to preserve and prolong the effective life of the battery. The problem we have is that we still have old habits from our days with previous types of batteries, and so there are many myths and misconceptions regarding how to properly handle a Li-ion battery.

Be careful of the discharge

You should not completely discharge the battery as soon as you have gotten it. On the contrary, it is better to recharge it continually. In fact, you should never completely discharge your battery, as you risk losing 20% of its capacity in one go! Operating systems generally shut down before the battery runs out of power precisely to avoid this problem, which comes from the fact that the accumulators are coupled to a complex electronic circuit that must constantly have power in order to keep track of and maintain the battery.

On top of this a total discharge leads to a chemical deterioration of the elements in the accumulator. Because of this, charging the battery (after a total discharge) can be potentially dangerous. This is why an internal circuit is in place to stop charging in order to avoid any accidents; although this also renders the battery unusable. It is not recommended to discharge your battery more than 95%, when possible.

Charge / discharge cycle

Contrary to popular belief, the number of charge cycles is not identical to the number of times you charge the battery. Confused? For example, your battery is at 50% of its charge. You charge it and it goes back up to 100%, then you unplug it again. You just recharged your battery twice, but two recharges of 50% correspond to only one recharge cycle. So, contrary to the popular idea, it is not necessary to wait for the battery to be empty to recharge it.

Actually, as we discussed above, the reality is quite the contrary. Finally, the battery should have a temperature between 20-45 degrees C whilst charging. Below this the lithium coats the electrodes, and above it the pressure becomes too high.

In both these cases the temperature can potentially render the battery unstable. Generally, if the charging temperature goes past 45 degrees C, a circuit cuts the charge, leaving you to think that the battery is full while it isn’t. The estimated optimal temperature is 20 degrees C; as we will see later on, temperature is an important element in the life of a battery. Therefore one must be particularly attentive to this detail.

With every rule there is an exception. During the first couple of uses of the battery, it is recommended to fully charge the battery then to leave it reach it’s critical state (5% of it’s full charge), without intermediate charges or letting it go below this percentage. Once the threshold is reached, recharge it completely. Contrary to popular belief, this procedure does not increase capacity. Rather, it is to tune the systems that measure the level of charge. This is what we call calibration, as this allows calibrating the system of measurement that will then be able to give a more accurate reading of the amount of power left in the battery. It is recommended to perform this calibration about once a month.

Normal losses

Lithium-ion accumulators will lose some of their capacity during the first ten cycles. It’s an unfortunate fact of life, but the loss is not too big (a few percentage points on the total). The battery also diminishes over time. The scale of this loss really depends on the materials used in the batteries construction and is therefore not the same for all batteries or systems.

The loss is explained by the process of manufacturing the Lithium-ion cell. At the moment it is made, the manufacturer applies a cycle of charge/discharge which forms a protective coat on the anode, but which consumes a little Lithium. This coat tends to thin with the first cycles; this causes it to consume a little more Lithium. Less Lithium logically means less capacity, although it is very difficult to determine at which point the accumulator losses some of its capacity, as this phenomenon varies with respect to the materials used.