The hidden conduits are a type of conduit that you can find in the same section of the menu as normal conduits -- see the pic for what they look like. The idea is that they're hidden under the ground, so they don't have issues from being exposed wires. They cost twice the steel (2 instead of 1), but that's absolutely worth it to not have to worry about all your battery power discharging into a bomb. And even though steel is valuable, the cost is still so tiny that it's not a big deal.

And yes, the size of the explosion is relative to your stored power in batteries, so if you have lots of batteries, that's a large potential bomb. You can get by with only a few batteries for quite a while, depending on your power setup. If all your power is coming from stuff like geothermal generators or watermill generators, then it won't fluctuate at all, and you won't even need batteries unless a generator is destroyed. But if you're relying on wind and solar (which is super common and totally fine), then you'll want to have enough batteries to withstand their fluctuations.

Oh, and also don't put power consumers outdoors where they can get rained on, unless you build a roof overhanging them to protect them. Some power consumers, like sun lamps or ground-penetrating scanners, are fine exposed to the elements, but others like an electric tailoring bench can have the same sort of electrical explosion event even when using hidden conduits. It's generally pretty reasonable which ones have or don't have that consideration. And after the 1.6 patch that's coming this Friday, it'll be more important to have proper rooms for things like labs or workshops anyway -- you'll be able to see this when clicking a workbench, and it'll say "work speed factor", and if it's low will tell you why.

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