[請益] 請問在這個句子中，what的功用為?

[zzss2003 (brotherD)]

原文:Since the scanner is cordless, its battery is its only source of power,
and since the scanner is intended to be handheld, the weight of the battery is
limited by "what" an average user can comfortably hold up.

我想請問一下，如果把What拿掉，在文法上是對的嗎?感覺這邊的What只有強調的作用。
那假使只有強調的作用，在中文上該怎麼翻比較好呢?

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