l = length of the wire (e.g. 10 m)
p = specific resistance (spoken: rho; copper = 0.0178 ohm x mm²/m)
I = current (e.g. 1A (ampere))
A= cross-section of the cable (e.g. 0.14 mm²)
If you used a fairly thin cable (0.14 mm² cross-section) for the extension, the total cable length amounts to 10 m, the voltage drop would be about 1.3V. Due to this drop it may be possible that the internal voltage regulator will no longer be supplied with sufficient voltage and thus does not work properly. Another cause might be a simple short circuit (direct connection from + to -).