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Chemical elements: capitalized or not?

Question:

I'm editing a technical text, and I'm wondering if chemical elements (in compounds such as nickel hydrogen battery) need to be capitalized.

Answer:

This case may be confusing because we capitalize the symbols for chemical elements. However, when writing the elements out in full, use lower-case letters. The Canadian Style confirms this rule.

Your example is therefore correctly written as nickel hydrogen battery. Or you could opt for the chemical symbols and write NiH battery.