Using NiMH Battery Charger To Charge NiCd Batteries (Explained)

The development of rechargeable batteries has been a great benefit to modern life. But, every convenience has a price. In the case of rechargeable batteries, the price we pay is chargers. Every battery type and voltage requires a different charger.

A Nickle-Metal Hydride (NiMH) battery SHOULD NOT be charged with a Nickel Cadmium (NiCd) charger. A 1.5-volt charger CAN NOT charge a 6.0-volt battery.

There are some “IFs” and “BUTs” to consider. I can shed some light on why the charger problem exists. I can also say that there may be solutions to some rechargeable issues.

Here are some key points from the article;

  • How Batteries Work.
  • Battery Chemistry.
  • Characteristics of Common Battery Types.
  • Charging Rechargeable Batteries.

Many rechargeable electronic devices have dedicated batteries and chargers. The battery is built-in and a charger is provided. Often the provided charger will have a proprietary plug that only fits that device.

In other cases, the charging port is a common USB port. In these cases, it is important to know the battery type and voltage of the device and the charger you are plugging into it.

Nimh Battery Charger
Using Nimh Battery Charger To Charge Nicd Batteries (Explained) 2

How Batteries Work

Batteries are electrochemical electron storage devices. In a charged battery, the negative terminal (anode) of the battery has an excess of negatively charged electrons.

The positive terminal (cathode) has a lack of electrons. Of course, the electrons want to be balanced. To stop the electrons from balancing within the battery, an electrolyte is used to separate the positive from the negative charges.

When the battery is connected to a device the electrons flow through it in their attempt to reach a balance. This creates the flow of current through the connected device.

Battery Chemistry

There are three common rechargeable battery chemistry styles today. From a use standpoint, they all function the same way. It is the internal chemistry of each battery type that impacts the charging and discharging function. The three are:

  • Nickle-Metal Hydride (NiMH)
  • Nickle Cadmium (NiCd)
  • Lithium Ion (Li-Ion)
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Each chemical combination allows for batteries to be built to nearly any voltage and milliamp rating. It is the charging, discharging, memory, and temperature sensitivity characteristics that are impacted by the internal chemistry.

Battery Characteristics

NiCd

NiCd batteries were the first rechargeable for home electronics. They are still popular in rechargeable hand tools. They have fallen out of favor due to the environmental concerns of battery disposal.

NiCd Pros

Today, the main advantage of NiCd batteries is their price. Years of production and competition have made NiCd the most affordable of rechargeables.

The biggest performance benefit of the NiCd is low internal resistance. This enables the NiCd to provide high surges of power. This makes them particularly applicable to hand tools, emergency lighting, and toys.

NiCd Cons

The NiCd battery does not provide the milliamp-hour rating of other rechargeable styles or even their alkaline counterparts. The cell voltage of NiCd cells is only 1.2 volts.

The voltage rate of NiCd is very linear but drops off quickly when the cell nears the end of the discharge cycle. This means the cells perform well, but die suddenly.

Trickle charging of cells is preferred, therefore NiCd cells charge relatively slowly. High and low temperature reduces their effectiveness.

NiMH

Due to their power-to-weight ratio, NiMH batteries have been instrumental in the development of hybrid and electric vehicles.

Their chemical stability makes them a more stable and safe energy storage device. The lack of cadmium made them an environmental alternative to NiCd.

NiMH Pros

NiMH batteries contain more energy per volume than other styles. This means a 1.2 volt NiMH will provide more milliamp-hours of energy in the same size package as other batteries.

They are also less prone to partial discharge memory issues. Under ideal conditions, NiMH batteries will provide 500 charge/discharge cycles. NiMH is more environmentally friendly than other rechargeables.

NiMH Cons

Due to their sensitivity to overcharging, NiMH cells need extra care when recharging. Charge times are usually longer than other styles. The self-discharge of NiMH batteries is higher than other chemistry types.

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They can lose up to 3% of stored energy per week. Charging and discharging in high or low temperatures can degrade the lifetime of the batteries.

Li-Ion

Li-Ion batteries are currently the state-of-the-art power storage device. They are in just about every personal electronic device and electric car on the market.

Currently, Li-Ion production costs make them more expensive than their counterparts. This is slated to change as worldwide production increases.

Li-Ion Pros

Li-Ion batteries are the latest rechargeable battery chemistry to reach the consumer. They deliver up to three times the power of comparably sized NiCd or NiMH cells.

They also have a higher rate of energy to weight ratio. The cells do not suffer from memory effects due to partial discharge. The self-discharge rate is below 2% a month. The lack of toxic cadmium has made Li-Ion an environmentally friendly alternative to NiCd cells.

Li-Ion Cons

They do require specific charging voltages to achieve proper operation. Overcharging can cause overheating and shorten the life of the cells. The main disadvantage of Li-Ion cells is their tendency to overheat. They also suffer from lost capacity over time.

What Can Charge What?

Built-In Batteries

When charging the built-in battery of an electronic device the charger provided with the device should be used. The charger is designed to work with circuitry in the device.

An after-market charger can be used if it is rated for the same voltage and battery chemistry. However, an after-market charger may not be as effective as the original charger.

NiMH Batteries

NiMH batteries should only be used with a charger designed for their chemistry. Due to the charging rates of other chemistry types, they would tend to overcharge NiMH batteries.

While a NiCd charger will charge NiMH batteries, it will be very slow and will eventually damage the battery.

NiCd Batteries

NiCd batteries can be charged with a NiMH charger. Due to the higher charge rate or NiMH batteries, the NiCd will charge fairly quickly and may not receive a full charge.

The NiMH charger may not detect that the NiCd is full and overcharge it.
Li-Ion Batteries Li-Ion batteries should only be charged with a dedicated charger. The voltage and charging current of Li-Ion cells are different than either NiCd or NiMH.

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If a Li-Ion is attached to another type of charger, either it will not charge at all or it will damage the battery.

Multi-Chemistry Chargers

Several tool companies produce multi-chemistry chargers for their products. DeWalt is one company that produces a smart charger that will charge Li-Ion, NiMH, NiCd battery packs for their products.

There are also smart chargers for AAA, AA, C, and D cells. These generally charge NiCd and NiMH. Li-Ion cells still require a chemistry-specific charger.

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