Compensation for using your own laptop at work

Hello guys, maybe someone already dealt with this: I work in a small but international company, and all swiss employees were asked to use our own laptops since company doesn’t have any. We know that it should be reimbursed, but how do we calculate the amount? We proposed to director chf50 per month compensation, and he claimed it’s too much, and that he’s ready to compensate something around 15-20 per month.