Patent ID: 7196495

Claim:
A power supply circuit comprising, a main battery ( 32 ) having a main battery positive terminal ( 32 B) connected to a bus (A), said main battery ( 32 ) supplying power only to a load ( 38 ), a predictive battery ( 30 ), independent of said main battery ( 32 ), having a predictive battery positive terminal ( 30 B), a battery monitor circuit ( 100 ) characterized by a reference voltage lead, a first input lead connected to said predictive battery positive terminal ( 30 B), a second input lead connected to said main battery positive terminal ( 32 B), and an output lead, and a light ( 50 ) connected to said output lead of said monitor circuit ( 100 ), with said battery monitor circuit ( 100 ) arranged and designed to cause said light ( 50 ) to illuminate only when respective voltage of both said main battery positive terminal ( 32 B) and said predictive battery positive terminal ( 30 B) are greater than a reference voltage of said reference voltage lead, said light ( 50 ) coupled to and receiving power only from said predictive battery ( 30 ).