LiPo batteries: charging, discharging and storage

Note: Thanks to Bastien for writing this article - https://forum.ircr.ch/

1. Charging

When charging a lithium battery, it is crucial to select the correct charging voltage and current, expressed as C-rate.

The charging voltage corresponds to the nominal value of the cells. A so-called “2s” or “2s1p” battery means it contains two 3.7V cells in series, for a total of 7.4V. When fully charged, the final voltage is 4.2V per cell, i.e. 8.4V for a “2s”.

The C-rate is the ratio between the charging current and the battery capacity (in Ah). For example, for a 6000 mAh (6 Ah) battery, charging at 1C equals 6A, and charging at 2C equals 12A. Note that LiPo batteries do not require break-in before first use.

It is recommended not to exceed a 2C charge to preserve the battery’s lifespan and maintain optimal performance.

Make sure to use a charger specifically designed for lithium batteries and follow the manufacturer’s instructions. Avoid overcharging or deep discharging, as these may damage the battery and compromise its safety. Never leave a battery charging unattended.

LiHV Battery: There are also so-called “HV” batteries for “high voltage”. These can be charged up to 4.3V per cell instead of 4.2V (8.6V instead of 8.4V for a “2s” battery). However, the vast majority of competitions or events (including IRCR) do not allow a final voltage above 8.4V (8.44V on voltmeter). An HV battery charges perfectly at standard voltage without any damage or performance loss.

2. Cell Balancing

When charging lithium batteries, especially multi-cell packs, balancing is essential to ensure safe and optimal usage. Balancing ensures that each cell in the pack is charged equally, avoiding potential imbalances between cells.

Due to slight differences in manufacturing and usage, cells can have different performance levels. Over time and after charge/discharge cycles, these differences may increase, creating imbalance.

To prevent imbalance, it is imperative to use a balancing charger suited for multi-cell lithium batteries (2S, 3S, etc.). A balancing charger has extra wires and ports to connect to each cell’s voltage measurement point and automatically balances the battery during the charge.

3. Storage

Before storing a lithium battery, partially discharge it to leave around 50% capacity. Keeping a fully charged battery for a prolonged period may cause premature performance degradation. Most modern chargers offer a “storage” mode that charges or discharges the battery to 50% capacity.

Ideally, store batteries in a dry place with ambient temperature between 10°C and 25°C. Avoid extremely hot or cold environments, as this can affect the battery’s chemical stability and shorten its lifespan.

4. Discharging (Not Recommended)

Besides storage, discharging can be used in charge/discharge/charge cycles during competition. These cycles aim to reduce internal resistance to improve performance. We strongly discourage such cycles for both leisure and competition use, as they accelerate battery wear for questionable gain.

5. Competitions

When participating in RC competitions, it is essential to follow specific rules regarding lithium battery usage. These rules are intended to ensure participant and public safety, and fair competition.

Competitions may set strict charge and discharge current limits for LiPo batteries. For example, some races may allow a maximum charge current of 10A or 12A, and discharge limits of 20A.

Before each round, it is common for organizers to check battery voltage to ensure compliance with regulations. Make sure your battery voltage complies with the event’s rules to be allowed to race.

In many RC competitions, the use of fireproof charging bags is mandatory during charging. These bags are designed to contain any potential overheating or failure during charge. Always have proper charging bags and use them as required by event rules.

6. Safety Precautions

Avoid overcharging or deep discharging lithium batteries.
Never use an unsuitable or damaged charger.
Never puncture or physically damage the batteries, as it may cause a short circuit.
Do not throw batteries into fire—they may explode or cause injury.
Keep batteries out of reach of children and pets.
Avoid handling lithium batteries with metallic objects that may cause a short circuit.
Follow the organizer’s safety rules regarding battery use at the competition site.