Most Richtek switching regulators have enhanced light load efficiency, thereby increasing the battery span.
Boost converters, such as RT9276 can be used to produce a stable USB 5V supply at varying battery voltage and provide battery monitoring function. Buck-boost regulators like RT6150A or RT6154A can be used when the output voltage lies in between the battery max and min voltage range, and with four internal switches, they seamlessly switch over from buck to boost mode. Most low voltage buck converters will operate in 100% duty-cycle mode when battery voltage approaches the output voltage, increasing the useful battery range, such as RT8059.
Low quiescent current LDOs like RT9063 can be used to regulate the output voltage for micro power applications with minimal battery loading. The 1μA ground current ensures minimal battery drain in low power standby mode.