alarm cable possible voltage drop?

hi, happy new year to all. my first project of the year is adding a second bellbox to my alarm. the current bellbox is texecom odyssey 3. so i have ordered another odyssey 3 to make it easier. i know how to wire them both together. there is currently a 6 core cable coming from the panel feeding the first sounder.

my plan is to move the cable which currently feeds the first sounder into a junction box in the wardrobe directly below, then from the junction box ill run a 6 core to each sounder. the first sounder is currently on sab so that draws approx 523 ma. the second sounder will be set to scb so approx 148 ma.

so here is the question will the alarm cable from the panel be able to support the 2 bellboxes on its own without too much voltage drop. the total draw on the cable will be 671 ma. the voltage is around 13.6v and the cable run is about 20 metres from the panel.

thanks in advance, sorry if it is too long