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FAQ for NiMH Batteries

  Low Capacity Issues
Q: I received the new NiMH battery, but after charge, I can't get the full capacity from the battery.
A: If you can get the right voltage but no full capacity, please follow the steps below:
1. Did you use the right charger ?
2. If so, please fully charge the battery several cycles, then you will get full capacity. It is the nature of NiMH batteries.
Q: We use NiMH cells to build a NiMH battery pack, why I can't get the same capacity of the sell ?
A: Assume you connect those cells in series. For example, if the cell's capacity is 10Ah, please expect the pack's capacity can only reach 80%-90% of 10Ah. This is caused of unbalance cells in the battery pack. The more cells inside the battery pack, the less capacity you will get, relatively.  So when you design a NiMH battery pack, please choose 20% higher capacity cells if your battery must run for certain time.
Q: I brought a new NiMH battery and after using for several times, it can't hold charge anymore. Why ?
A: You might over discharge the battery. When using NiMH batteries, please stop use it when you feel it getting weak, especially for RC car batteries, Airsoft Gun batteries, etc.  You need to charge it immediately. Please never discharge below 1.0V/cell.
  Charge the NiMH Batteries
Q: What kind of charger should I use for NiMH Batteries ?
A: You must use NiMH charger for NiMH batteries.  Some Nicd chargers can charge NiMH batteries, but some can't. Please DO NOT use other type of charger, like Lithium charger/LiFePO4 charger/etc., to charge NiMH batteries because the charge algorithm is different. If wrong charger is used,  it might cause explosion.
Q: How does NiMH charger work ?
A: Most of NiMH charger using Negative Delta V (-ΔV) algorithm to monitor if the battery is fully charged or not.  When a battery reaches its full charge, its voltage decreases slightly. The -ΔV will detect the small voltage drop and stop charge the battery.  Due to the electronic noise and voltage fluctuation, sometimes -ΔV can't detect the small voltage drop accurately, it might stop charge earlier before battery is full. That is another reason you might not get 100% capacity from NiMH batteries.
  Shelf-Life / Self-discharge / Maintenance Issues
Q: I brought a new NiMH battery, I didn't use it very often. After a while, I found my battery is dead , why ?  What is the shelf-life of NiMH battery ?
A: NiMH batteries can self-discharge over time. Self-discharge is caused by internal chemical reactions. The self-discharge rate varies greatly with temperature, where lower storage temperature leads to slower discharge rate. The self-discharge is 5-20% on the first day and stabilizes around 0.5-4% per day at room temperature.

If you do not plan to use NiMH batteries for a while, please fully charge them every 3 months to maintain your batteries.
  Basic Knowledge
Q: What is mAh or Ah ?
A: mAh or Ah is the measurement of energy storage capacity of the battery. mAh means mili Ampere Hour, Ah means Ampere Hour.  For same size battery, the more capacity the better, because it can run for longer time. If a battery has 1000mAh capacity and another one has 2000mAh, the second battery can provide 2x using time, of course, it will take 2x time to charge, assume using the same charger.
Q: Do NiMH batteries have memory effect ?
A: Nim batteries do not have memory effect.
Q: What is cycle life of NiMH battery ?
A: If you use NiMH battery properly (charge and discharge within battery's specification, no over-discharge under 1.0V/cell, immediate charge after use), it will last for 500-1000 cycles, which is around 2-3 years. Besides, the more you use and charge NiMH battery, relatively the more cycles you will get.
  Please also read Safety Instructions for NiMH Batteries

-- Updated on 2/22/2017
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