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Do I Need To Discharge My NiMH Batteries For My RC Car?

If you want to know if discharging your NiMH battery is necessary keep reading. Also, learn how to maintain your battery and if they lose charge when they are not being used.

Do I Need To Discharge My NiMH Batteries For My RC Car?

No; you do not need to fully discharge your NiMH batteries before recharging them. NiMH batteries are much less susceptible to the memory effect than NiCd batteries, and regularly fully discharging them can be harmful and reduce their overall lifespan.

It is generally recommended to recharge NiMH batteries when the power of your RC car starts to decrease. However, it is still a good idea to fully discharge your NiMH batteries once every 3-6 months to help recalibrate them and keep them performing at their best.

The Memory Effect

The ‘memory effect’ is a phenomenon that occurs in NiCd batteries when they are repeatedly partially discharged and then recharged. This can cause the battery to ‘remember’ the partial discharge level and then only provide power down to that level, reducing its overall capacity.

To combat this, it was often recommended to fully discharge NiCd batteries before recharging them. This practice was so common that it has carried over to NiMH batteries, even though they are much less susceptible to the memory effect.

How to Maintain NiMH RC Batteries

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Here are some helpful measures:

Proper Storage

It is essential to store your NiMH batteries properly when they are not in use. Store them in a cool, dry place, away from direct sunlight and heat sources.

It is also recommended to store them in a partially charged state, about 40-50% of their capacity. Avoid storing fully charged or completely discharged batteries, as it can lead to reduced capacity and performance over time.

Regular Usage

Regular use of NiMH batteries is crucial to maintaining their performance and longevity. If you leave them unused for extended periods, they may develop a condition called ‘voltage depression’ or ‘memory effect,’ which can lead to reduced capacity and run time.

To avoid this, try to use your NiMH batteries at least once every two or three months.

Proper Charging

Proper charging is vital to maintaining the health and performance of NiMH batteries. Use a charger designed specifically for NiMH batteries and follow the manufacturer’s instructions carefully.

Avoid overcharging or undercharging your batteries. Overcharging can lead to overheating and reduced battery life while undercharging can lead to voltage depression or memory effects.

Avoid Deep Discharges

Deep discharging, or draining the battery completely before recharging, can lead to reduced capacity and battery life. It is recommended to recharge your NiMH batteries when they reach about 20-30% of their capacity.

Some modern RC devices and chargers come with a low-voltage cutoff feature that automatically stops the discharge at a safe level.

Keep Them Cool

NiMH batteries perform best at room temperature. Avoid using or charging them in extremely hot or cold conditions. If your RC device gets hot during use, allow it to cool down before recharging the batteries.

Do NiMH Batteries Lose Charge When Not in Use?

Yes. For NiMH batteries, the self-discharge rate is relatively high compared to other rechargeable batteries like Lithium-ion.

A typical NiMH battery can lose about 20-50% of its charge in the first 24 hours after being fully charged, and then it continues to lose about 10-20% of its remaining charge per month thereafter.

This means that if you fully charge a NiMH battery and then store it without using it, it may only have about 50-80% of its original charge after one month, and even less after several months.

What is Self-Discharging of NiMH Batteries?

Self-discharge is a phenomenon where batteries lose their charge even when they are not connected to any device or load. All rechargeable batteries, including NiMH, experience self-discharge to some extent.

The rate at which a battery self-discharges depends on various factors such as the battery’s capacity, its age, and the temperature at which it is stored.

Factors Affecting Self-Discharge of NiMH Batteries

  • Capacity: Higher-capacity NiMH batteries tend to have a higher self-discharge rate than lower-capacity ones. For example, a 2500mAh NiMH battery may have a higher self-discharge rate than a 2000mAh NiMH battery.
  • Age: As NiMH batteries age, their self-discharge rate increases. This is because the internal resistance of the battery increases with time, leading to higher energy loss.
  • Temperature: The self-discharge rate of NiMH batteries increases with temperature. Storing NiMH batteries at lower temperatures can help to reduce the self-discharge rate. For example, storing a NiMH battery at 0°C (32°F) can reduce its self-discharge rate to about half compared to storing it at 20°C (68°F).

How to Minimize Self-Discharge of NiMH Batteries

  • Store at Low Temperature: Storing NiMH batteries in a cool place, such as in a refrigerator (but not a freezer), can help to reduce their self-discharge rate.
  • Use Low Self-Discharge NiMH Batteries: Some manufacturers offer low self-discharge NiMH batteries, also known as pre-charged or ready-to-use batteries. These batteries have a lower self-discharge rate compared to regular NiMH batteries and can retain up to 85% of their charge after one year of storage.
  • Recharge Before Use: If you have stored NiMH batteries for an extended period, it is advisable to recharge them before using them to ensure they have sufficient charge.