What you�ve got to factor in is that, running off the �sidelight� circuit (on a stock bike) are:

Sidelights (2x 5W front, 1x 5W number plate and 8x 0.5W LEDs in the tail light) = 19W/1.52A @ 12.5V
Indicators (2x 10W) = 20W/1.6A
Hazards (4x 10W) = 40W/3.2A

Now you aren�t going to have the hazards and the indicators on at the same time, so we�ll assume the �worst case scenario� power consumption/current at 12.5V (battery voltage) is 59W/4.72A if you use the hazards. Which leaves you 66W/5.28A spare capacity on this circuit.

Most USB chargers and GPS/sat nav cradles need approximately 2-3A to charge a flat power cell (and draw 500mA even when nothing is plugged in) and most heated kit is 2-4A per item. This doesn�t leave a lot of room for manoeuvre.

You can �buy� yourself an extra 12W/0.96A by fitting LED bulbs to the front sidelights and number plate lamp (also LED indicators would help, but only with an electronic relay, not resistors), and obviously when the alternator is charging the circuit voltage will be 13.6-14.4V, which will lower the current flowing by about 10%. At best, with everything LED and with the engine running you could maybe achieve spare current capacity of about 9A on the sidelight circuit?

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