They are the most popular rechargeable batteries being produced in standard sizes such as AA, AAA etc. They are considered as the most suitable replacements of the alkaline batteries in many applications. The voltage of each shell is 1,25 Volt. This voltage is lower than that of the alkaline (1,5 Volt) but higher of the Ni-Cad (1,2 Volt).
Advantages: High capacity, come in standard sizes, easy to be charged.
Disadvantages: More expensive than the Ni-Cad, they lose their charge quickly when not in use and are not suitable for use in high energy ‘’thirsty’’ systems.
Differences between Ni-MH and hydride Ni-MH batteries.
Both types are rechargeable 1,2 Volts systems being interchangeable between them. The main difference is the hydrogen absorption ability from the alloy which is used in the anode of the hydride Ni-MH batteries (negative electrode) which replaces the cadmium electrode being in use in the Ni-Cad batteries. Usually the Ni-MH batteries have better performance and they are environment friendly as they do not contain cadmium which is a heavy metal.
How many times the hydride Ni-MH battery can be recharged?
The life time expectance of a battery depends on a series of factors such as the construction method, usage plan and storage conditions. Ni-MH batteries are more sensitive to prolonged charge than the Ni-Cad, which ends up to a shortened ‘’life’’ time if they are always submitted to extent charge. Also storage in a high temperature environment will lead again to the same shortened life time. With proper handling today’s Ni-MH batteries can be charged and discharged for hundreds of times.
Why batteries become hot during charging?
It’s a normal procedure due to the energy that the charger ‘’pumps’’ in the battery during the charging cycle. Generally, the faster the charge the higher the temperature. At the end of the charging cycle the battery’s temperature should drop to normal (room temperature) within a few minutes.
How long Ni-MH battery remains charged?
Latest generation batteries have been improved to such an extend so they maintain their 70% of their initial charge for a 6 months period of time, being storaged in a normal temperature environment.
Life time expectance.
Up to 5 years, if properly storaged. After a prolonged storage period several charging/discharging cycles are advised to ‘’wake them up’’ .
Batteries condition check.
Due to their constant discharging is difficult to define a certain quality check for the Ni-MH batteries. For fully charged batteries a battery checker which measures the voltage in a closed circuit may be used as a general guide to define if the battery is usable or defective. A voltmeter which measures the voltage in an open circuit is not reliable, so it is not recommended. The best way to measure their performance is to monitor the time and the voltage during a controlled discharging.