Variable speed of light ( VSL ) theories generically lead to large violations of charge conservation that can be written in terms of a dimensionless parameter \lambda .
It is shown that the motion of the Earth with respect to the Sun could lead to a seasonal variation for the SAGE and GALLEX-GNO experiments and analyzing the reported counting rates for these experiments , a very stringent bound \lambda \leq 2 \times 10 ^ { -19 } is obtained , some 10 ^ { 9 } times smaller than previous ones .
Furthermore , a bound on the lifetime of the \hbox { } ^ { 71 } { Ga } \to \hbox { } ^ { 71 } { Ge } charge-nonconserving decay in VSL theories is found as : \tau _ { CNC } \geq 1.4 \times 10 ^ { 27 } { years } .
Similarly a new upper limit for the ratio of the charge-nonconserving to the normal weak decay of the neutron in VSL theories is obtained : \Gamma ( n \to p + \nu _ { e } + \bar { \nu } _ { e } ) / \Gamma ( n \to p + e + \bar { \nu } _ { e } ) \leq 2 % \times 10 ^ { -27 } .