How do I charge the cap while traveling abroad / overseas / in a foreign country / in a country with different voltage?
The REVIAN cap is a dual voltage rated device, which means you do not need a power (voltage) converter for international use, but rather only an adapter for the plug/socket type of the country to which you are traveling.
The REVIAN cap charges via USB 2.0 with a dual 100-240V input range, so countries with standard voltages in that range (such as the UK, where the standard is 230-240 V) will not need to be converted. REVIAN conducted a clinical study in Australia for two years where the cap was charged with 240V input, for instance, and the UK and Australia both have a standard voltage of between 230-240 V. You'll just need to use an adapter for the plug/socket type of the country to which you are traveling.