A backup UPS will not last for 6 months. The backup started is probably designed to provide just high power for small amount of time (jump start)
Your best bet will probably be an additional regular battery connected to the jump start terminals under the hood. (In this case you'll have to keep the hood opened).
I've left mine parked for 2 months with no issues at all, but to be honest with you for 6 months I'll definitely unplug the battery and then deal with the reprogramming with the dealer. Electronic circuits usually go crazy with low voltage.
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