While there are many advanced battery monitors available that count ampere hours to display state of charge (by using a current measuring shunt), one drawback can be their accuracy over extended time periods. If you are prepared to periodically re-synchronise your monitor, then the Merlin PowerGauge Lite and Pro are good examples. If however, your application is such that manual re-synchronisation is not possible or practical, Merlin SmartGauge is the ideal solution.