First, if you're using Eelektross in any tier higher than RU, stop using it. Better volt switchers: Alolan Raichu, Zapdos, Raikou, mega Manectric, Magnezone, wash Rotom, heat Rotom, Galvantula, both Thundurus forms, Xurkitree
If you're using it in a format where Eelektross is actually good, give it 252 HP/252 SpA/4 SpD modest. The max special attack is for obvious reasons. Its speed is really low, so putting EVs in it won't do much good. If you distribute the remaining EVs among both defenses, they go up by 1.16 times, which means Eelektross will take 1.16 times as many hits. If you use the remaining EVs to max HP, its HP will go up 1.20 times, which means Eelektross will take 1.20 times as many hits. It's a small difference, but it's still better to invest in HP.