AA/AAA NiMH batteries are very common in daily life, but they have strict charging requirements and can easily be undercharged or overcharged. Overcharging the battery can cause excess energy to turn into heat, causing the battery to get hot severely and damage the internal structure.

So, how can we better charge NiMH batteries? XTAR’s unique CVSA technology (NiMH Charging Voltage Slope Analysis) offers a solution.

Understanding the Challenges of NiMH Batteries Charging

Charging NiMH batteries is more complex than charging Li-ion batteries because their peak voltage drops slightly once they are fully charged. Traditional chargers use the “Negative Delta V” (negative voltage change) method to detect whether the battery is fully charged, but the voltage change for NiMH batteries is usually only 3-5mV.

This small change makes it more difficult for chargers to detect accurately. If the charger isn’t accurate enough, it may cause stop charging early or overcharge the battery, affecting its performance and lifespan.

XTAR CVSA Technology Solutions

To address the above problems, the XTAR team developed CVSA tech and integrated it to our smart chargers. The key advantage of CVSA is that it controls the battery temperature during charging to avoid overheating, while also ensuring faster charging and higher accuracy of full-charge detection. This helps prolong the lifespan of NiMH batteries.

Additionally, chargers with CVSA tech don’t rely on a single method for full-charge detection, but use multiple methods, including over-voltage protection, timeout protection, and -delta V detection, ensuring a safer and more efficient charging process.

Experimental Verification: The Effect of CVSA Technology

The XTAR lab conducted a comparison test on NiMH batteries of different brands using a charger with CVSA tech and a charger with -delta V detection only. Here are the test results:

From the table, it’s clear that CVSA tech shows a significant advantage in charging NiMH batteries:

• Faster Charging Speeds and Lower Battery Temperatures: In most charging tests, CVSA tech can shorten charging time and effectively control the battery temperature. For example, when charging a XTAR #3 AAA NiMH battery, the charging time was reduced by up to 115 minutes, and the temperature was lowered by 11.6℃. This shows that CVSA can optimize the charging process, improving charging efficiency while generating less heat.

• Multiple Protections to Avoid False Full Charge and Overcharge: When charging an Eneloop and Camelion AAA NiMH batteries, the benefits of CVSA tech may not seem obvious, as the charging time was 6 minutes longer, and the temperature was slightly higher. In fact, this happened because the battery wasn’t truly fully charged. It also highlights the limitations of the -Delta V detection, which relies on a single full-charge detection and is prone to interference, causing the battery to not be fully charged.

On the other hand, CVSA tech can more accurately assess the battery’s condition. While the time may be a little longer, it helps prevent false full charges or overcharging, and make the battery is truly fully charged.

Real User Feedback in Practice

》 Garry Purcell from Australia：CVSA tech enables faster and more full charging.

Garry did a comparison between the XTAR L4 charger and the EBL charger when charging NiMH batteries. From his video, it can be seen that the L4 delivers battery voltages of 1.44V and 1.46V when fully charged, while the EBL charger results in voltages of 1.37V and 1.4V. This indicates that the L4 can charge the NiMH batteries more fully. Besides, the EBL charger took about half an hour longer than the L4.

》 Dr. Gough Lui from Australia：CVSA tech enables gentler NiMH charging.

Goughlui tested the CVSA charging algorithm of the XTAR L4 charger and found it to be very gentle when charging NiMH batteries, without causing noticeable temperature increases. Whether charging one or four cells, the L4 showed consistent charging curves. The CVSA charging algorithm implemented results in a pulsed charging current waveform, and the LED lights turn green after about 4 hours, indicating that the battery is fully charged. If the battery isn’t removed immediately, the charger will continue to deliver a small amount of current after 2 hours. Even when charging four cells at once, the peak current stays below 1A.

Moreover, Goughlui observed that during the first 10 minutes of charging, the activation/trickle current of the L4 averaged about 190mA. Throughout most of the charging process, the average pulsed charging current was around 450mA, with the battery voltage slope significantly increasing towards the end, reaching a peak of about 1.52V. In reality, XTAR chargers limit the maximum charging current for NiMH batteries to 500mA, which is also largely to help protect battery performance.

XTAR latest VX4 charger also uses CVSA tech. According to the test of Electronic Passion from France, the NiMH battery during charging is about 26.7℃, while the heat dissipation area of the charger is about 29.8℃. This fully proves that this technology can ensure safe charging temperature.

Conclusion

CVSA tech provides a safer and more efficient charging experience for NiMH batteries. Compared with traditional charging methods, it not only shortens the charging time, but also effectively prevents the temperature rise caused by overcharging, thereby extending the battery life.

XTAR has upgraded and optimized most chargers that support NiMH batteries and introduced CVSA tech. If you want to better protect and use your NiMH batteries, XTAR chargers are definitely worth a try!