If the cost of electricity is not a concern to you, and if you have no commitment to extreme notions of ecological responsibility, store your working Compact AIOs indoors on shelves, attached to the mains but not turned on, so as to maintain trickle power. That results in battery life equivalent to their shelf lives, and minimizes the temperature extremes that outdoor storage may induce.

I have more than thirty Macs from CRT iMacs to Compact AIOs in my study (in a temperate coastal climate), and all of them are functional. More than twenty are in a LAN and ready for instant startup. Non-functional Macs I keep without power or batteries in an outdoor brick garage.

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