Nickel-metal hydride (NiMH) batteries theoretically do not have a memory effect. For batteries that have experienced capacity reduction due to the memory effect, we can repair most batteries by repeatedly charging them fully and then discharging them completely. For batteries that have been stored for a long time and have lost their activity, we can try to reactivate them by applying a high-current surge.
Because the main characteristics of nickel-metal hydride (NiMH) batteries are low internal resistance and high discharge current, many digital cameras currently use 1.2V NiMH batteries for power. In particular, digital cameras powered by 3V batteries only have a voltage of 2.4V when using two NiMH batteries. The instantaneous current when the camera is turned on can reach more than 2A. At this time, if the internal resistance of the old NiMH batteries is high, it will cause the voltage to drop instantly. The camera's detection circuit will mistakenly think that the battery power is insufficient, which will cause the battery power to not be fully used up or the camera to fail to turn on.
I had several sets of NiMH batteries that I'd used for nearly two years. Now, even after a full charge, they only have half a bar of charge left when I turn on the camera. After leaving them for a week, they sometimes won't even turn on, although they work fine in other devices. Analysis suggests that after prolonged use, an oxide layer forms on the internal electrodes of these old NiMH batteries, increasing their internal resistance. Therefore, these batteries are no longer suitable for digital cameras with high starting currents. Reducing the internal resistance of old NiMH batteries is key to reactivating them. During use, I discovered that discharging these batteries with increased internal resistance using a high current activates them.
The specific procedure is as follows: First, charge the NiMH battery normally. Then, connect two NiMH batteries in series in your hand. Use a digital multimeter set to the 20A current range. Short-circuit the positive and negative terminals of the NiMH batteries directly with the multimeter probes. At this point, the shunt resistor in the 20A current range of the digital multimeter and the probe leads become the load for the NiMH batteries. The resistance is very small, only a few tenths of an ohm. Observe the current indicated by the multimeter; it will gradually increase and stabilize above 4A. The NiMH batteries will also slowly heat up. When the temperature of the NiMH batteries feels around 40 degrees Celsius, stop discharging. After the NiMH batteries return to normal temperature, start discharging again. Repeat this cycle until the voltage of each NiMH battery drops to 1V, completing the discharge process. Then, charge the NiMH batteries normally again. Generally, a NiMH battery can be used normally after one discharge cycle. If it cannot be used normally, repeat the discharge cycle again. NiMH batteries that cannot be activated after three discharge cycles should be discarded. This method is not suitable for new NiMH batteries and may shorten their lifespan.
When your battery life gets shorter (due to memory effect or aging), do you buy a new one to replace it? Next time this happens, save your money and try this very effective method:
1. Wrap the battery in newspaper, then put it in a plastic bag, seal it tightly, and freeze it for three days (the newspaper can absorb excess moisture).
2. Remove after three days and leave at room temperature for two days.
3. Charge the battery two days later, and once fully charged, test it in a mobile phone (estimated recovery rate: 80%-90%).
This information was revealed by an engineer from a well-known battery manufacturer, and friends who have tested it report that the effect is quite effective.
As for whether it will work or not, the battery is almost dead anyway, and everyone has a refrigerator, so you guys might as well give it a try!
The memory effect of nickel-metal hydride batteries is quite obvious, so I thought I'd try discharging it first before making any decisions. I used a multimeter to measure the positive and negative terminals of the 2611 battery; the two ends of the battery are the positive and negative terminals. The voltage was 10V, which seemed normal. After a complete discharge, the battery had a high chance of recovering. Now, I started discharging it. I disconnected the AC power, turned on the computer, and saw the battery level: 98%. I opened Winamp and listened to MP3s for twenty minutes, then the computer prompted me to save my work. At this point, the battery level showed 1%. The computer quickly went into hibernation mode. I shut it down, removed the battery, and measured the voltage again—strangely, only 10V! I ignored it and found two 6V emergency light bulbs. I plugged one into the power source, and the bulb was unusually bright. I left it like that for now. After nearly two hours, the bulb finally went out (I later discovered it was burnt out). I put the battery back in, plugged it into the AC power, and turned on the computer. The power management showed it was charging, and in about 5 minutes, it was already 60% charged! How could this be??? In about half an hour, it was fully charged. I started the "BatteryBar" test, which showed 100% battery. After disconnecting the AC power, BatteryBar showed 98% remaining battery, with an estimated usage time of 3 hours and 10 minutes. I was secretly pleased: "Could this be enough? So easy!" I started Winamp to listen to music, but less than ten minutes later, an alarm sounded! "Low battery, please replace the battery." The battery level showed 3%, and then the computer went to sleep. This time, the battery only lasted ten minutes. I removed the battery and checked the voltage; it was still 10V. It seemed the battery wasn't discharging properly. I had no choice but to plug in a light bulb and wait. After about 5 minutes, the light went out, and the voltage was still 10V. What was going on? It seemed the battery hadn't decreased at all. I checked the light bulb; it was burnt out! This couldn't continue. I put the battery back in, disconnected the AC power, and started the computer. Surprisingly, it started! The battery level was still 3%. Then came the rapid alarm sound, and the computer went to sleep. Now, I was deep in thought. Since the battery could still start the computer, it was clear the battery had sufficient power. The computer quickly went into sleep mode after startup, indicating that the battery discharge was uneven, not that it was completely depleted. Therefore, the remaining power should be enough to start the computer. Let's try this: while the computer is in sleep mode, click the mouse to activate it, then activate it again a while later. This might improve the discharge efficiency. The computer went to sleep and woke up every three minutes. After 45 minutes of this, the computer finally wouldn't wake up. I removed the battery; this time the voltage was less than 5V. I connected a 6V light bulb and continued discharging until the bulb went out, indicating successful discharge. I reinstalled the battery, connected it to AC power, and turned it on. The power management display showed: charging, 1% charge. I opened Word to write this article and noticed the charge display remained at 1%, but the battery area was warm to the touch, indicating it was charging. After waiting for 1 hour and 50 minutes, the charge displayed 43%. I couldn't wait any longer and decided to test it first. Disconnect the AC power, launch "BatteryMaxiMiserWizard," set the battery to medium power saving (CPU speed: medium, LCD brightness: Level 7, highest screen brightness), and start measuring battery life. Run Winamp and Word in the background. CPU usage was 100%. The battery drained relatively smoothly: it took 2 minutes to go from 43% to 37%, 9 minutes from 37% to 31%, 9 minutes from 31% to 25%, and 10 minutes from 25% to 3%. The actual battery usage time was 30 minutes, consuming 40% of the battery. Proportionally, a fully charged battery should last about 80 minutes. Thus, the battery is perfectly restored. This result truly surprised me; I never expected that such a seemingly primitive method could give my old battery a second life. This, in a sense, demonstrates the quality of IBM laptop batteries. IBM laptop users who have encountered the same problem as me can try this!
Discharge the battery completely after it's completely empty!
Depending on the battery condition, you can either short-circuit it directly or use a 1-ohm resistor as a load to discharge it until the terminal voltage is close to 0V, which generally takes 5-10 hours. This can prevent the battery from being accidentally short-circuited and burned out after adding water, and it can also reduce electrochemical corrosion during immersion in water.
Open the safety valve. Batteries from brands like Sanyo and Sony have four holes at the positive terminal, through which the rubber cap of the safety valve can be seen.
Bend a piece of thin iron wire (I used a 1/4-inch resistor lead) into a U-shape, and then insert it about 2mm from the bottom of the rubber cap towards the center. This forces the safety valve to open. The U-shape is to avoid damaging the rubber cap.
Scald the battery with freshly boiled water until the positive terminal stops bubbling, but do not boil the battery!
Immediately drop the bottle into cool (room temperature is fine) purified water and wait for about 1 minute. At this point, some water will have been absorbed. Then, tighten the cap and squeeze the bottle for about 10 seconds to allow more water to enter the battery.
Remove the battery, dry it, pull out the U-shaped wire, and reseal it. It's best to use a large Phillips screwdriver and a small hammer to slightly dent the center of the positive terminal cap to increase the safety valve's seal. A dent of 0.5mm is sufficient; denting too much is dangerous!
After 5 hours of resting, begin 3-5 charge-discharge cycles. For the first charge, use a fast charger (I chose a Panasonic BQ390) for about half an hour, then use a slow charger (I used a 100mAh AGP power bank) until the terminal voltage reaches above 1.45V (this takes a long time). After that, you can use a medium or slow charger (I used a Sony BC-CS2A).
The final step: recapacitance. Here, I first fully charge the battery and let it sit for 5 hours, then use a "ZB210 multi-functional battery capacity tester" to discharge it at 1A with a constant current until the end, and then mark the capacity (accurate to 10mAh, rounded) on the battery with a paint pen.
