Characteristics of D Batteries | Voltage, Capacity & Self-discharge (2024)

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D Battery

A D battery, also known as an R20 battery, is one of many types of single-cell cylindrical batteries. D batteries are large batteries, that are typically used in medium-drain applications such as large toys,flashlights, and musical instruments. They have significantly higher capacity than AA and even C batteries.

Several different chemistries are used in their construction. The exact terminal voltage, capacity and practical discharge rates depend on cell chemistry; however, devices designed for D cells will usually only take 1.2-1.5 V unless specified by the manufacturer.

Types of D batteries:

Primary Battery

• alkaline battery
• lithium metal battery
• zinc-carbon battery
• zinc-chloride battery

Secondary Battery

• NiMH battery
• NiCd battery

Cell Voltage

The voltage of electric batteries is created by the potential difference of the materials that compose the positive and negative electrodes in the electrochemical reaction.

Alkaline batteries have an open cell voltage of about1.5 V. A common open circuit voltage for NiMH batteries (e.g. C and D) is 1.2V.

Cut-off Voltage

The cut-off voltage is the minimum allowable voltage. It is this voltage that generally defines the “empty” state of the battery.

When testing the capacity of a NiMH or NiCd battery, a cut-off voltage of 1.0 V per cell is normally used, whereas 0.9 V is normally used as the cut-off voltage of an alkaline cell.

Capacity

The coulometric capacity is the total Amp-hours available when the battery is discharged at a certain discharge current from 100% SOC to the cut-off voltage.

A typical alkaline or NiMH battery in the standard “D” size has about10000 (NiMH) to 15000 mAh (alkaline).

C-rate of Battery

C-rate is used to express how fast a battery is discharged or charged relative to its maximum capacity. It has unitsh⁻¹. A 1C rate means that the discharge current will discharge the entire battery in 1 hour.

To obtain a reasonably good capacity reading, manufacturers commonly rate alkaline and lead acid batteries at a very low0.05C, or a 20-hour discharge.

Self-discharge

Batteries gradually self-discharge even if not connected and delivering current. This is due to non-current-producing “side” chemical reactions that occur within the cell even when no load is applied.

One of the main advantages of alkaline batteries is that they are easy to store. They are chemically stable, and they have a very low self-discharge rate. Alkaline batteries typically lose 2 to 3 percent of their original charge per year when stored at room temperature (20–30 °C). The NiMH battery also has high self-discharge and can lose up to 20 % of its charge during the first 24 hours and thereafter 10 % per month.

Degradation

Some degradation of rechargeable batteries occurs on each charge-discharge cycle. Degradation usually occurs because electrolyte migrates away from the electrodes or because active material detaches from the electrodes.

The cycle life for NiMH batteries is typically700-1,000 life cycles.