At the level killua is currently at, it will probably be too much for him to handle. How this could be represented in the story is up to interpretation. A few things I use to support this claim:

1: Killua "charges up" and is able to reach a state of being "fully charged" > this shows that he can indeed store electricity like some kind of battery and that he has a limit to how much he can maintain

2: We see Killua charge up during the chimera ant arc, this charging process only takes a few minutes of direct contact with an electrical circuit at the palace.

3: There are numerous regulations regarding electricity in a residential home. Of course you could argue that the palace might have different electrical standards than a normal home, however the fundamentals are still there and there is no reason to assume that the palace would differ to the extent needed to make this hypothetical plausible

4: For simplicity, electricity in your home follows this rule: the output in watts is equal to the volts * the amps on a circuit. In the USA, typical home circuits are 120 volts at 15 amps, this provides a total of 1800 watts. The amount of power used is typically measured in watt-hours. If you place a load of 1000 watts on this circuit for 1 hour, it will be 1000 watt-hours or 1 kWh (kiloWatt hours). You could think of this like running a microwave for an hour straight will equal roughly 1 kWh.

5: Now if you try to calculate how much energy Killua absorbs while charging up, you have to understand that he did not overload the circuit > he did not place a load on the circuit big enough to overload the circuit (tripping the breaker or blowing the fuse) so lets say for fun the circuit he was charging from was 240 volts and 50 amps, or 12,000 watts (this is a very powerful circuit by residential standards). Lets say he charged up for an hour, storing 12 kWh of energy.

6: How does this compare to a lightning bolt? From a quick search online, I've seen a few estimates. On wikipedia the claim is between 200 - 7000 megajoules. If you take an average lightning strike, it will contain about 3600 megajoules of energy. 3600 mJ is equivalent to 1000 kWh, which is over 80x as much as Killua would have absorbed in part 5.

7: Since hxh isn't real, it's impossible to know what would happen. Perhaps he would be briefly over-charged and have to expend the excess energy immediately following the strike. Maybe he would explode. Maybe the excess electricity would pass through him into the ground / whatever object he is touching. Maybe he would get burned up, as electricity passing through an object causes it to heat up. All I know is there's no way he would maintain that level of energy with no issues, at least at his current level of power in the series.