Hi!
Every one over here uses some form of diod checker. We mount them in every airplane we have! The left one in the pictures below has two diods ..one green and one red.
Green diod lights: means everything is alright, green and red diod lights...beware ...Red diod lights: do not fly!
At home I have a multimeter which I check the voltage on each cell when I'm not certain of the battery pack. 1,1-1,25 volt is OK, 1volt or under is not. I naturally do this with the battery under load (some servos connected)!

Regards!
Jan K
Sweden