| Word | Description |
| R | resistance |
| Rapid Charge | The charging of a battery, typically a NiCad, to its capacity in a short period of time |
| Rapid-Charge Battery | A battery pack that is designed to accept a high amount of current in a short amount of time, such as a radio-control battery |
| Rate Sensitivity | Typically refers to battery performance under various discharge loads with operating voltage being the defining characteristic |
| Rated Capacity (Dry Cell) | The average capacity delivered by a cell or battery on a specified load and temperature to a cutoff voltage, as designated by the manufacturer. Rated capacity is usually determined by an accelerated test approximating the cell or battery's capacity in typical use. |
| Rated Capacity (Flooded) | The CCA, RC or amp-hours that a battery can deliver at a given rate of discharge, end voltage and temperature. These ratings are often displayed on the outside of the battery |
| RC | reserve capacity |
| Rechargeable Battery | A cell or battery capable of being recharged. Refers to secondary batteries |
| Recharging | See charging |
| Recombinant | The process in which the oxygen formed at the positive (+) plate diffuses to the negative (-) plate, reacts with the lead and suppresses water loss. In a recombinant (immobilized electrolyte) chemistry battery, gassing is recombined within the sealed battery so that water addition is unnecessary |
| Reconditioning | See Conditioning |
| Rectifier | Device that changes alternating current to direct current |
| Rectify | To convert alternating current into direct current |
| Reserve Capacity (RC) | BCI defines it as "the number of minutes a new, fully-charged battery at 80ºF (27ºC) can be discharged at 25 amps and maintain a voltage equal to or higher than 1.75 volts per cell" (i.e., 10.5 volts for a 12-volt battery). This rating represents the time the battery will continue to operate essential accessories in the event of a charging system failure. |
| Resistance (R) | The opposition to the free flow of current in a circuit. Resistance is measured in ohms. See also Internal Resistance |
| Resistor | A device, with electrical resistance, that is used in an electrical circuit for current control and efficient operation. |
| Reversal | See Reversed Polarity |
| Reversed Polarity | The changing or reversing of the normal polarity of a battery, which commonly occurs when battery cables or charging cables are connected backwards |
| Ri | internal resistance. |