Battery trickle charger connections

The pig tails I use are just long enough to hang the end connector outside with the trunk closed. This way, I can make and break the connection with the car locked, which is convenient if I'm not driving the car for a while. It also will allow the charger to break free, if I'm knucklehead enough to forget about it and drive off withe charger lead connected.

The fact that your battery tester can sense the excessive lead length is why you should keep the charge lead length as short as practical. Most smart chargers perform similar tests before and during charging to gauge the battery's state of charge and state of health.

Volfy said:

It also will allow the charger to break free

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You could even get a magnetic breakaway connector, if you really wanted to make it foolproof (ideally with some kind of strain relief on the car-side connection...could be as simple as a knot that won't fit through a gap when it's yanked).