NiMH Battery Charging Tips - Introduction, Need, and Overcharging

Batteries have numerous applications and are needed for several types of everyday use objects. Generic or low qualities are good for the short run but they fail to offer value for heavy-duty or even long-term usage. 

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NiMH or Nickel – Metal Hydride batteries are a great option with regards to discharge efficiency and cycle durability. These rechargeable batteries are can last for 5 years or longer with careful usage and healthy charging and discharging practices. These NiMH batteries can be recharged hundreds of times and still work just fine offering high efficiency. 

Here are some great tips for charging your NiMH battery in the safest possible way:

Trickle Charging – It the best way to charge your NiMH battery to keep it healthy and performing at its best. Always use a low current charger and let your battery charge until full. However, do not keep your battery hooked up to the charging port for over 20 hours. Whether the battery is fully charged or not, you have to stop at 20 hours and give it some rest. This way your battery will be automatically protected against overcharging. For newer versions of NiMH battery, trickle charging is not the way but still using the modern fast charger is not feasible. The common smart chargers that do not heat up the battery are safe up to any limit.

Stop If the Battery Heats Up – NiMH batteries cannot be allowed to heat up while charging or it will render the battery chemicals useless and seriously diminish the battery capacity. Try to charge the battery at room temperature. Also, it would be prudent to check in from time to time while the battery is charging. Check it by touching the battery to see if it is warm. If the battery feels normal to touch or at room temperature, let it charge otherwise unplug and let it cool. Then start recharging after a short while.

Avoid Overcharging – The battery cannot be left plugged in after it is fully charged. It negatively impacts the battery in every imaginable way. But it is also not feasible to keep checking it every five minutes so; the easiest way to protect your NiMH battery against overcharging is to use a smart charger. These chargers stop the current supply after the battery is fully charged and you do not have to fuss over anything.

Memory Charging – NiMH batteries have memory charging which means they remember the last charging cycle and use it as a base for the next charging. So, they had to be fully discharged and fully recharged for this feature to remind the battery of the level it needs to charge at. If any battery is not charged properly as specified it charging capacity diminished with every cycle which eventually will lead them to perform so poorly that is simply not worth using anymore.

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What Current Should You Charge Your NiMH Battery?

AA/AAA NiMH batteries can be charged up to their capacity generally indicated as 1C. The current at which your battery can be safely charged is 2000mAh. This battery type does well with trickle charging and the ideal current for that is 0.05C. If you charge your battery using a charger of these specifications then your battery will run smoothly for a really long time. However, some diligence is required while selecting the battery charger. This particular type of battery performs well and lasts much longer if it is charged using low current chargers that are easily available in the market. Smart chargers detect changes in voltages and temperature of NiMH batteries and can easily signal a full battery or stop supplying current.

Do NiMH Batteries Need To Be Fully Discharged Before Charging?

If you care about your NiMH battery’s health and expect it to work fine at least up to its expected life which is 5 years, you have to fully discharge it before you can recharge. Also, you have to recharge it to full before you start using it for the same reason. Originally the NiMH batteries had a memory system which meant they had to be fully discharged before charging otherwise they would charge or discharge only up to the last defined charging or discharging limit. This means the in discharged portion will not charge afterward and will be rendered useless. However, this was the case with older battery versions. The newer ones do not need to be fully charged or discharged. But still, the same capacity diminishing effect is observed if the battery is not used and charged fully every time. So, it would be wise to try and finish the power as much as possible.

Can You Overcharge a NiMH Battery?

Yes! NiMH batteries are prone to overcharging generally because of user impatience or unhealthy charging practices. If the charger is too powerful or has the wrong voltage, it will overcharge the battery and damage it permanently. So will, leaving the battery plugged in for a longer duration than advised. These are wrong but commonly used ways of charging these batteries that will lead to overcharging and damage the performance and ultimately the battery itself. Some users do not charge or discharge these batteries properly. For example, plugging in the battery before it is fully drained or removing the charger before it is fully charged and discharging it. These batteries have a memory and they need to be fully charged and discharged for long-term usage and reasonable performance expectations. Besides, overcharging will heat up not just the battery but also the charger and render it or both useless. It is also a waste of electricity. So, overcharging these NiMH batteries is a wrong idea all the way and a smart charger can help make things easy to maintain but some diligence on the user’s part is still required.

These are all the dos and don’ts that can either improve your NiMH battery life significantly or damage it to no use. How well your battery performs depends on how carefully you are using it.