NiMH Battery Charging Tips

While the research for NiMH batteries began in the 1960s, it wasn't until the 1980s that they became practical for real life application. NiMH batteries have much in common with NiCd (or Nickel Cadium) batteries in that both are Nickel based batteries. NiMH batteries are Nickel-metal-hydride and are related to NiH (Nickel-Hydrogen batteries, which are used in satellites. Understanding a few tips for charging NiMH batteries can help users to get the most from their batteries.

 

While different types of batteries have different characteristics, there are a few things that are true of all batteries in terms of extending their useful life. Extreme temperatures are enemies of batteries. Refrigeration can extend a battery's life, though. Discharging a battery completely is generally harder on the battery than a partial discharge. However, with nickel batteries occasional full discharge helps to prevent battery memory (see Section 3).

 

NiMH batteries are not fully formatted when they arrive from the manufacturer. In order to achieve full effectiveness, the batteries need to be charged and discharged a number of times. That number varies depending on the manufacturer, but can range from single digits to a hundred times. Manufacturer's recommendation calls for charging new batteries 14 to 24 hours before initial use. That process allows for multiple batteries to achieve an equal charge level.

 

Battery memory effect refers to something called "voltage depression." It refers to a phenomenon in which batteries are recharged before becoming fully discharged and it causes the battery to "remember" the lower charge level and only accepts a charge to that level. It is not very common in NiMH batteries. You can prevent battery memory effect by fully discharging NiMH batteries once every one to three months and then fully charging them.

 

When charging, NiMH batteries will become warm. The batteries should be allowed to cool before use. Overheating can damage NiMH batteries. Make sure the charger used includes a temperature sensor to avoid overheating. NiMH batteries should not be charged when hot because it can prevent a full charge. When not in use, NiMH batteries should be stored in a cool place. They can be stored charged or discharged, as neither condition will affect the performance of the battery.