CTek charger - eyelet connectors

Yeah he does say that for the bench demo he will use the negative terminal but does state clearly you use an earth / ground point when the battery is in a car.
Watch from 30sec to 60sec mark in the video.

We use cTek in the boat and have done for many years. Left on all winter to manage the batteries. Boat is fiberglass so no concept of body earth, we have the eyelets connected to the boats charging VSR and it's fine.

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As Chris said.
I will second that electrically it makes no difference, the battery -ve terminal and body earth points on the Jimny are at the same potential.

I guess they are trying to keep any possible arching sparks that may occur when connecting away from the battery terminals, and any vented gas, as they also say connect the -ve body clamp last. This puts the potential spark area away from the battery. Just a guess on my part.

Over cautious world's in which we live maybe.

Mike

Thanks all. Seems likely I’m over-thinking this

I would connect it directly to battery, at the M10 nut.

The reason for choosing a chassis earth rather than battery post is probably more to do with modern car electronics over spark mitigation.
With a lot of cars nowadays having start/stop and smart alternator technology, they generally have some form of shunt on the battery earth connection which allows the ECU to monitor the amount of charge in the battery to allow for dumping charge into the battery on regen when going downhill.
If you were to charge the battery bypassing this shunt, the ECU would be unaware of the recharge, so it is best to connect to the chassis side of the shunt so that any external charging from a battery charger is able to be seen by the ECU and taken into account when the car is started following the charging. Have a look for a small OEM wire connection off the negative terminal to check whether it is fitted with a current monitoring shunt, if it has, then I advise not connecting direct to the battery terminal but to the chassis side of the shunt instead.
Modern vehicle electrical systems are a real pain, my VW Transporter needs to be reprogrammed with battery type and capacity if the battery is ever changed so the charging system can work out the best way to use its capacity and monitor/adjust the way it charges the battery as it degrades over time.