State of charge battery monitor

A monitor for monitoring the state of charge of a battery of the type having an electrolyte which maintains a substantially constant specific gravity notwithstanding variations in the state of charge of the battery, said monitor comprising:

• an enclosure within the electrolyte defining a cavity, said enclosure being at least partially formed from a substantially non-permeable charge transmissible material;
• a fluid medium within said cavity, said fluid medium comprising a material which exhibits a varying specific gravity responsive to the charge therein and arranged to assume therein the charge of the battery electrolyte by the passage of charge from the electrolyte through said substantially non-permeable charge transmissable material while being substantially separated from the electrolyte;
• specific gravity detecting means immersed within said fluid medium for sensing the specific gravity of said fluid medium and thus the state of charge of the battery;
• and indicating means coupled to said detecting means for providing an indication of the state of charge of the battery responsive to said detecting means.