There are a few key differences between a 51R and 35 battery. The first difference is in the size of the battery. A 51R battery is significantly larger than a 35 battery, making it able to hold more charge. This means that a 51R battery will last longer than a 35 battery, making it ideal for use in high-drain devices such as digital cameras. Another key difference is in the voltage of the two batteries. A 51R battery has a higher voltage than a 35 battery, meaning that it can provide more power to devices that require it. Finally, while both batteries are rechargeable, only the 51R battery can be fast-charged. This means that you can recharge your 51R battery in less time than it takes to recharge a 35 battery.