If all "Batteryman C"(s) on your side of the field are in Attack Position, increase the ATK of all Machine-Type monsters on your side of the field by 500 points for each "Batteryman C" on your side of the field. If all "Batteryman C"(s) on your side of the field are in Defense Position, increase the DEF of all Machine-Type monsters on your side of the field by 500 points for each "Batteryman C" on your side of the field.
From Battery Charger's effect, it was obvious there were going to be more Batterymen. Batteryman C works best when you have three of them face up in the same position (Enemy Controller can cancell out this effect) they will increase the attack or defense (whichever one they all are in) of Machines by up to 1500 for 3 of them.
But being Thunder types, they don't power themselves up, and with 0/0 for attack and defense, it's hardly worth it to have three 0 attack monsters out to power up up to 2 machines...
The best way to use this (if you do) is to combine DNA Surgery, so at least you have 3 1500 attackers and +1500 to your other monsters