| Word | Description |
| DC | direct current |
| Deep Discharge | The discharge of the battery to below the specified cutoff voltage before the battery is replaced or recharged. |
| Deep-Cycle Battery | A battery that is designed to withstand repetitive discharges to a 20% depth of discharge or more and to continue providing its rated capacity after hundreds of cycles. Deep-cycle batteries are often used in marine/RV and industrial applications. |
| Depth of Discharge (DOD) | The percent of rated capacity to which a cell or battery is discharged. It is the reciprocal of a battery's state of charge. Example: a battery that has a depth of discharge of 45% has a state of charge of 55%. |
| Digital Voltmeter (DVM) | See voltmeter |
| Diode | A semiconductor device that acts like a one-way valve for current. Today's alternators use diodes to rectify current. |
| Direct Current (DC) | An electrical current that flows in one direction only. A battery delivers direct current, discharging the battery, and is recharged with direct current. |
| Discharge Rate | The rate at which current is drawn from a battery, usually expressed in amps. |
| Discharged | The state of a battery when it has less than a 100% state of charge. Levels of discharge are shown in the Open-Circuit-Voltage Chart. |
| Discharging | The withdrawal of electrical energy from a cell or battery, usually to operate connected equipment. A battery is discharging when it delivers current. |
| Distilled water | If the water level in your battery is low, Interstate Batteries recommends adding nothing but distilled water to a vehicle battery. No other additives have been proven to extend battery life and may actually decrease it. |
| Drain | Withdrawal of current from a cell or battery. Often referred to as discharging. See also Average Drain and Initial Drain. |
| Dry Battery | A battery in which the electrolyte is immobilized, being either in the form of a paste or absorbed into the separator material. |
| Dry-Cell Battery | A cylindrical-cell battery, typically nonrechargeable and disposable, such as a standard alkaline, heavy-duty or general-purpose battery. See also Cell. |
| Dual-Alloy Battery | See Low-Maintenance Battery. |
| Dual-Terminal Battery | An automotive battery with top terminals and side terminals. |
| Duty Cycle | The time duration and use frequency during which a battery is drained. It is affected by such factors as charge and discharge rates, depth of discharge, length of cycle, and length of time in standby mode. |