The entire idea of the batteries being replaceable has "fallen out of canon" so to speak. While it was an element that made the weapons more alien in the first game, it would have drastically changed gameplay and confused some players if it was changed in the second. By the time Halo 3 came around (and, in canon, the humans are now allied with Elites, and should therefore have all of the same information and least know how to collect and replace the battery, even if they don't know how to recharge it), it had become a relic of an ancient game manual.
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