Doesn't surprise me that you get a peak current when you first reconnect the battery.
Cars are full of computers that all want to reboot at the same time if they have had a period with no power.
Unlike the old days switching the ignition off does not disable as much as you might think and there are a lot of circuits that are still live and doing stuff.
After the initial spark of battery reconnection does the current drop off after a few minutes once all of the systems have re-initiated themselves?
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