Both batteries started displaying error flash

[zinznader]

Both of my Dewalt nicd batteries started doing the rapid error flash at the same time (i.e one displayed it pulled it off and the other did the same) when they had previously been working perfectly. Is there a way to check whether it is the batteries or the charger, without having to find another battery to try out the charger. My colleagues all use  HILTI so I cant easily check it that way