Coulometer battery state-of-charge indicator
A. G. Birchenough, R. R. Secunde · NASA Technical Reports Server (NASA) · 1970
Mercury-column electrochemical coulometer is a linear ampere-hour integrating device consisting of a sealed glass tube containing two columns of mercury separated by a gap containing an electrolyte. The drive circuit uses operational amplifier techniques to match nonlinear charge-discharge characteristics of an alkaline battery.