Is there any difference between a 3.6V and a 3.7V battery?

In general, a 3.6V nominal voltage battery and a 3.7V nominal voltage battery are essentially the same thing. The nominal voltage of a battery is the average voltage output that a battery provides over its discharge cycle. It is not a fixed value and can fluctuate depending on the state of the battery's charge.

The difference between a 3.6V and 3.7V nominal voltage battery is usually just a matter of rounding. In most cases, a 3.7V battery is simply a newer or more recently manufactured version of a 3.6V battery, and the nominal voltage has been rounded up to 3.7V for marketing purposes or to better align with industry standards.

It is worth noting that the actual voltage of a battery can vary depending on several factors, including temperature, load, and age. Therefore, it is important to check the actual voltage range and specifications of the battery to ensure that it is suitable for the device or application it is intended for.