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I thought of those but they're pretty expensive ($40+) compared to just a 7AH UPS battery ($20). The capacities are a bit misleading too, since a 7AH 12V battery gives you 7AH at 12V and the lithium jump starters are at 3.7V, so an 8000mAh pack is actually 2466mAh at 12V and probably closer to 2000mAh after boost efficiency conversion. They also might have built-in cutoffs to prevent them from being used continuously at 12V output. The problem with the 12V UPS battery is that you need a lead-acid charger as well so there is a definite advantage on the jump packs there.