Charging NiMH Batteries for the First Time- Charging Hours and Discharging

Charging Nickel Metal Hydride batteries play an integral part in ensuring great performance. The batteries and cells should usually be charged rightly and kept under required conditions to guarantee the long life of the batteries. Moreover, knowing the correct procedure for charging NiMH batteries will ensure its higher performance. Effects such as overheating or damaged cells are highly possible if you do not perfectly charge your batteries. In addition, it is also important to know the best time to discharge and charge your batteries to ensure maximum efficiency.

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How long does it take to charge a NiMH battery?

There are different ways to charge NiMH batteries correctly; overnight charging, fast charging and many more. These methods will fully charge a NiMH battery at other times. Therefore, it will depend on how fast you would wish your battery to charge.

Parallel Charging

Parallel charging is one of the fundamental ways to charge various Nickel Metal Hydride battery. You will find that the delta-V bump that usually indicates when the battery is fully charged is pronounced inadequately in NiMH than in NiCad. Furthermore, new NiMH can develop bumps in the curve in the early stages. Again, when the charging rates exceed C/10, NiMH becomes sensitive to overcharge. Therefore, if the charging rate is kept steady at C/10, the NiMH battery will take 10 hours to charge to capacity. As a safety precaution, it is advisable that you disconnect the battery after a full charge to prevent overheating. The best way to detect if a NiMH has fully charged is using a thermostat to measure the heat formed at the electrodes.

Overnight Charging

Overnight charging is one of the cheapest methods to charge a NiMH battery. This method will only require a charging rate of C/10 or 10% less rated capacity. Overnight charging does not need an end of charge detector but ensures a full charge. Moreover, contemporary batteries feature a catalyst that recycles oxygen to prevent any further overheat. With all the charging conditions laid into consideration, a Nickel Metal Hydride battery will take 13-15 hours for a full capacity charge. Nevertheless, using the time while charging is paramount for overcharging slowly reduces the efficiency of the battery.

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Faster Charging

Using this method to charge a NiMH is quite risky since it requires that the battery be completely discharged before initiating the charging process. If you happen to charge your battery when it is 90% of capacity, venting the battery is likely to happen. To ensure that venting does not take place, discharge the NiMH battery and turn the charger on. Following these procedures step by step, the Nickel Metal Hydride battery should charge fully in 5 hours. Furthermore, if you introduce a temperature monitor while charging will charge the battery in 1.5 hours.

How do you charge a new NiMH battery?

There is nothing as hard as charging a brand new NiMH battery. However, you have to consider some guidelines and conditions before charging a new Nickel Metal Hydride battery. 

Firstly, you should use an incorrect charger to charge a new NiMH cell: note; all NiMH batteries. Generally, it is unacceptable to charge any form of battery using a faulty charger. For example, if you use a NiMH charger to charge a NiCad charger, the end-of-charge detection will be effective. Therefore you should always use the right charger for your batter. Moreover batteries such as lithium and Nickel usually require unique charge algorithms. Also, NiMH is sensitive to charging conditions compared to other rechargeable batteries.

Secondly, it is normally recommended to check the charge status of the new NiMH manually. It should be done frequently since there is a higher possibility of overcharge with new NiMH with many lower ends. Furthermore, sometimes these batteries may lack the backup for a lot of charge ability. Therefore, it is prudent to confirm if the battery is fully charged and charging is disconnected.

Another thing, not all new NiMH batteries exhibit fast charge features. Checking whether the battery features quick charge capabilities should be a priority. Confirm on the spreadsheet before placing the battery on a fast charge. Most importantly, it is usually wise to note that batteries should be charged at normal room temperature.

Finally, every battery has its own way of preventing overcharge. Overcharge prevention is a key factor to consider while charging a NiMH battery. A battery with no overcharge prevention measures will slowly lose its efficiency with time. Provided the charging current is kept constant, there are several techniques you should consider if you ever wish to prevent this overcharge. These are timer charging, thermal detection, negative delta voltage detection and slow charging NiMH batteries.

Should NiMH batteries be discharged before charging?

This question of whether the NiMH should be discharged completely before being charged again is hard to understand. Well, it is not significantly okay to remove a NiMH battery before charging them. Under normal operation, NiMH has features the same characteristics as its counterparts NiCad. Nevertheless, some charging method requires that batteries should be discharged to one cell per hour. Therefore, considering the process of charging, the battery may be discharged or not. However, Nickel Metal Hydride batteries are not suitable for discharging and high-rate discharging. Under normal conditions, NiMH releases at a maximum rate of 3C.

Nonetheless, over-discharge may be quite dangerous to your battery. Over-charging causes reverse polarity in the cells, permanently damaging the battery. Other than over-charge, self-discharge and low self-discharge is also damaging if not put into consideration.

In conclusion, batteries, in general, are very sensitive when it comes to charging. A battery would require many factors to be placed together for long-life performance. Knowing the correct manner in which every battery should be charged should be of great importance. Moreover, discharging a storm is normally not acceptable as it causes some damages to the battery. For new NiMH batteries, if you are not sure of the charging capabilities of the battery, just confirm on the spreadsheet.