All batteries produce around 2 volts (sometimes a little more or less depending on the type). To make higher voltage battery packs, manufacturers link identical batteries in a series circuit. Six 2-volt batteries linked together become a 12-volt battery (6 x 2 = 12). This is an easy electrical technique that you can do at home with simple math and no special equipment.
You can also wire multiple 12 volt batteries together in parallel connection to get enhanced current or Amp Hour capacity while keeping the voltage at same level as one battery's. This is the typical method used in car batteries and many cordless power tools.
D-size batteries are larger than the AA and AAA dry cell batteries and come in both primary and rechargeable types. They are cylindrical in shape with spring terminals at both ends. They can be found in flashlights, paper towel dispensers, automatic odorizers and transmitters among other high drain devices. D batteries are a household essential.
When a D battery is charged, it becomes warmer because more energy is being put into the cells. Over time, this can lead to a "memory effect" where the battery loses some of its capacity when repeatedly charged before it is fully depleted. This can be avoided with a good quality charger that monitors various battery parameters and keeps the battery at its full charge state.
Proper care and storage of D batteries is important. They should be kept in a cool dry place away from extreme heat or cold. They should also be charged in a timely manner. The faster they are charged the better their performance will be. If you are unsure whether the battery needs to be charged, a good battery hydrometer will tell you.
