wobbly plug and apparently sensitive to shutdown

I have connected a cooler for the car. First, notice that you have to both terminals wobble slightly and turn until a reliable contact connection exists - which can be fatal during a long drive with cooler when here suddenly no longer flows ...
In a short test I also noticed that even happen with the engine running, several shutdowns when the cooler starts and this obviously takes a little more current. My car battery is a little older, but is working on reliably - with running alternator must not happen at something; without the battery monitor the cooler running wonderfully and this (I have not tried it for longer - the engine started after 1 h with no abnormalities) loosely 1h without alternator. Ergo the battery monitor is counterproductive for me. Then I look at the clock, or rather let the cooler only with laufenem engine cool ... :(