72V can charge with 9V because the 9V source has a higher potential difference than the 72V battery. When connected in parallel, the 9V source will push current into the 72V battery, causing it to charge. This process is possible because the voltage of the charging source needs to be higher than the voltage of the battery in order for the charging to occur. **

To charge a 72V battery, you will need a charger specifically designed for that voltage. Make sure to use a charger that is compatible with the chemistry of your battery (e.g. lead-acid, lithium-ion). Connect the positive and negative terminals of the charger to the corresponding terminals on the battery, making sure to observe the correct polarity. Follow the manufacturer's instructions for the specific charger you are using, and ensure that the charging process takes place in a well-ventilated area and is monitored for safety. **

To connect 72V NiMH battery packs in series, you will need to connect the positive terminal of one battery pack to the negative terminal of the next battery pack. Repeat this process until all the battery packs are connected in a series. Make sure to double-check the polarity to ensure all the packs are connected correctly. Finally, you will have a series connection of 72V NiMH battery packs. **

No, camera batteries cannot be effectively charged with 72V via USB. Most camera batteries are designed to be charged with a specific voltage and amperage, usually 5V via USB or a specific charger provided by the manufacturer. Charging a camera battery with 72V via USB could potentially damage the battery or the camera itself. It is important to always use the recommended charging method and equipment provided by the manufacturer to ensure the safety and longevity of the camera and its battery. **

No, the 72V-74V battery does not only start charging at 9V. The 9V mentioned may be the minimum voltage required for the battery to start charging, but it will continue to charge as long as the voltage remains within the acceptable range. Once the voltage drops below 9V, the charging process may stop until the voltage rises again. It's important to monitor the voltage levels and ensure that the battery is charged within the recommended parameters. **

A 72V motor cannot be directly operated with a 9V battery due to the significant difference in voltage. In order to operate a 72V motor with a 9V battery, a voltage step-up converter or a DC-DC boost converter would be required. This device would increase the voltage output from the 9V battery to the necessary 72V level to power the motor. It's important to note that the current output of the 9V battery must also be sufficient to meet the motor's power requirements. **

To operate a 72V 2500W motor, you would need 6 12V batteries connected in series to achieve the 72V required. Each 12V battery would need to have a capacity of at least 416.67Ah (2500W/72V). Since 100Ah batteries are available, you would need 5 of them to achieve a total capacity of 500Ah, which would be sufficient to power the 72V 2500W motor. **

The capacity of the charger for a 72V battery with 500mAh would depend on the charging rate of the charger. If the charger has a charging rate of 1A (1000mAh), it would take approximately 30 minutes to fully charge the battery (500mAh / 1000mAh = 0.5 hours). However, if the charger has a lower charging rate, it would take longer to fully charge the battery. It is important to match the charger's capacity with the battery's capacity to ensure efficient and safe charging. **