Arrguh! that’s terrible news. I do all my own work on my cars and its a fear of mine dropping the bonnet on to tools left around the engine bay.
A permanent fused connection with fly lead off the battery helps avoid this too. My C-Tek chargers had this kit as a low cost option. worth doing.
I don’t work for or sell C-Tek by the way! :0)
Yes my CTEK came with this optional flylead well worth having makes it so much easier to use without the risk of any damage etc.
Hi
CTEK are very good I leave one car on all winter and two others on charge when we go on extended vacations. Never had any problem.
They are also supplied as an extra for Aston Martin, a Freud did have a problem with his ——- he drove off with it still plugged in and ripped the socket out of the wall. 
The CTEK I’ve just bought comes with this flying lead with eyelets, and I see that one can buy additional ones. Is there any downside to permanently fitting one to each car’s battery?
Notwithstanding the current lockdown, as SWMBO I are both now retired, I can foresee the cars being somewhat “less used” than before.
Good Evening All,
or you could buy an EV…
Regards
Richard
Just make sure rubber cap is firmly inserted to keep the water out when not in use to prevent any shorts. 
It does make life all easier especially if you have more than one car.
CK
I have them on all my cars, it was especially useful on my classic car which didn’t see much use during the winter. They dont cause any issues, just tuck them away safely and make sure the ‘bung’ is firmly in the open socket when not in use.
Being retired from Ford i always remember the cars returned from management had a few dings. Well the guy that sorted them, eventually retired…he was a great guy. He was Asian…Singh the ding, was how he liked to be known as…frightening to watch and hear him at work. But like magic, think his son does this now in Essex.
No downside to permanently fitting the flying lead, with its plug fitted when not in use.
On my Porsche Boxster, I read on a forum that you need to connect the earth lead to the car’s body & not directly to the negative battery terminal. I’m not sure what the reason is for this, but there happens to be a very convenient threaded hole on the adjacent suspension tower.
Hi tony, the “finding a negative connection away from the battery” may be when jump starting from another battery or high power booster rather than for trickle chargers. It a common request for other car brands. Either way connecting via a good negative point on the car won’t make any difference to a trickle charger
BMWs use a tag or bolt to the chassis for mounting the negative terminal. It’s never connected to the battery terminal. It works fine with a CTEK.
Hi Roog, I really couldn’t see why one should avoid connecting directly to the battery. If there wasn’t a convenient alternative I confess I’d have just whacked it on there. I’ll have to look up the relevant postings.
I agree, no problem connecting to the battery lugs
In terms of the Porsche seems to be something about the battery management system. I Found this below on a ‘Porsche site’. Plus the CTEK youtube video says the CTEK should not be connected to the neg pole of the battery.
Having said all this and I need to investiate a bit more but connecting direct to the battery as it seems most folks do works OK.
If you connect any charger to the battery direct you bypass the battery management system … in other words it won’t know the state of charge for the battery … a lot of it is calculated by the car with power in / out being measured .
If you have a CTEK and its not wired this way then go back to your garage … the Earth MUST be on the body and NOT on the neg lead of the battery .
The above is reiterated by CTEK at 0.40 mins in this clip.
Interesting, it would be helpful to know why it matters.
Mind you his advice isn’t exactly very sensible, telling people that it doesn’t really matter if you get the connections the wrong way around. Ok so C-Tek chargers may have protection built in but it is hardly a good habit to get into.
A little project for me today. Nice to have the time to devote to these things.
Agree with pdc. Fit and forget, but remove before yoy star the car!
I got one of those CTEK 5.0 chargers a few months back to use on my modern Mercs as they have AGM batteries. The newer Mercs have dedicated charge points: a flat positive terminal over which slides a protective plastic cover, and a negative/earth pole. Seems to work well.
I’ve also long used a Mercedes branded CTEK charger on my classic SL which lives in the garage and comes out rarely. It only does a few hundred miles each year and when in the garage is permanently connected to the charger using the standard crocodile clips. In over eight years it has always started on the first turn of the key, and the battery wasn’t new when I got the car. So I can highly recommend the CTEK chargers.
Interesting, and useful to know. Fortunately, both our Audis are so old they don’t have such new-fangled technology; both manuals state “connect to the battery terminals”, which is just as well…coz that’s exactly what I did 
BMW say connect under the bonnet (hood) at the designated terminals or directly at the battery terminals located under the boot (truck) floor.
However a word of caution when charging directly to any battery when its on the car, apart from the rule of always connecting the earth (-) neg terminal last & disconnect it first, try to connect (-) neg to a chassis/body bolt & not to the battery - why ??? if for whatever remote reason you do get a spark, a spark at some distance from the battery avoids the possibility of the battery gas igniting. I’ve done that a few times when working on battery storage & repair & believe me its not funny.