Incredible.....
I just got this notice from Hagerty...
"All it takes is a battery to get overcharged, or a wire to get rubbed a few too many times and cause an arc and suddenly there’s fire. It often happens silently and causes damage quickly.
Check your chargers or tender regularly to see if they are warm to the touch or otherwise defective. If possible, unplug them when not needed as it will minimize the risk of something melting down without you being there to catch it."

Just my $0.02...

It is a risk versus reward.

Reward is a few more months of battery and risk is multi thousand $ fire or death.

In the fine print of the insurance policies have they slipped in “no battery tender” wording?

My hot rod runs a walmart battery gussied up with some decals and fake red caps.

I just disconnect it and remove it from the car and set it in the warm basement for the 3 or 4 months of winter. So far no issues.

I used to run a battery tender but I've decided the (very small but potentially catastrophic) risk is not worth the marginal benefits on a cheap-o battery.

Yeah, cause that is the difference. Ask Rhino if insurance made him completely whole. That it replaced all the personal stuff that mean nothing to insurance policies but everything to you. Did it recompense him for all the aggravation and time he spent dealing with it and, God forbid, had a loved one died what price could you ever put on that?

CTEK

CTEK - 40-206 MXS 5.0 Fully Automatic 4.3 amp Battery Charger and Maintainer 12V

I used a battery tender on my race car for years when its home in the trailer but last year the green light was on indicating good when in fact the battery was bad and had to be replaced . I don't use the tender much anymore maybe on my winch battery once in awhile.

I use a CTEK MUS 4.3 POLAR battery charger/maintainer. Works great, no issues at all.

https://smartercharger.com/products/ctek-mus-4-3-polar

The battery charger/maintainer sold by Mopar Parts is manufactured by CTEK.

https://store.mopar.com/oem-parts/mopar-battery-charger-82213378ab

the charger i am using now is one of those pulse types that is supposed to do ????????
anyway, i just hook it up and charge away when i'm in the garage.
then, to make sure i unplug it when i go in the house, i have it hooked to a bright orange 14ga outside extension cord that is plugged into an outlet that is next to the door into the house. i can't miss that, so that works for me.

What about the battery chargers for tools? Are they safe to leave plugged in?

Probably not.

My fire was due to a 19.2V Sears cordless drill battery. I had one in the charger fully charged and put the dead battery in the charger when I found out it was completely dead. It only took 5 minutes to catch the garage on fire beyond any chance of putting it out. Apparently the dead battery had a dead short in it and the charger thought it was charging the battery, instead in got hot real fast and ignited papers and old broadcast sheets I had sitting next to the charger. I had it plugged into an old power strip straight into an outlet that went right to the breaker box. I DO NOT leave a battery being charged without me being there to watch it, especially for the first few minutes I plug it in. The insurance company (State Farm) did me good. The only things I did not get reimbursed for was my used and NOS parts since I did not have receipts for them, which was a significant loss! However they did pay for every one of my tools, but I had to buy them first then give them the receipts. I also had a collection of factory brochures from the 40's to the 90's that was lost, they paid me $5K for them, who knows how much I had in them over the years. The nightmares and agrivation still goes on today, I will never get fully over it...

I found out the drill chargers STILL draw a current with no battery plugged in, ALL stay unplugged till I need them. Another thing, key fobs on cars that have the push button starters. IF they are hung up within 30-50 feet of car the battery in fob will die. Seems inside that 50 feet the fob and car ‘talk’ to each other continuously till battery dies. Never leave it in car

A ready to be discarded microwave might offer a lot protection as an enclosed charging station.

I got in a habit of keeping chargers unplugged many years ago and after so many stories I’m glad I did. I think one was warm one day without a battery in it is why I started doing that.

The key fob thing is interesting. The spare key to my wife’s car is kept in a cabinet probably 25 feet away from the garage spot. I use it when I take it out about once a week. Today the car flashed the low battery warning again, I thought I must be getting junk quality batteries. Maybe not. I’ll move it and see how the new battery does. At my last house the batteries went forever, we had a detached garage then. Thanks.

I have noticed that the newest power tool battery chargers have changed design
and moved the 120AV to DC low voltage “switching power supply” to the wall plug,
where it can be made more flame resistant cheaper because there is less material.

It also makes the larger Lithium battery holder where wet dirty human hands touch often free of 120V AC and lowers lethal shock risk.
Old design long wall cord that had 120 AC becomes lower DC voltage.

I am speculating their insurance companies made them make that redesign.

I don't see any real advantages here of wall/outlet mounted with those changes except maybe lower manufacturing costs.
Maybe better convection cooling of being on an elevated vertical surface rather than a flat surface?
I personally discount the concerns of wet/dirty/120V aspects.

Happy New Year Moparts , The US Coast Guard has the on FIRE and BURNING Vessel "Genius Star XI ", anchored 2 MILES off the shore from Anchorage Alaska filled with Dangerous and
Unstable Lithium-Ion Batteries . At least when that Flaming Vessel finally Sinks , it's 2 miles from Beautiful Dutch Harbor ! Genius Star XI has been Burning since Xmas Day !

My fearless New Year prediction:

Just like the “bad guys with tech smarts”
quickly figured out how to unlock the doors and start the car
by hacking into the computer BUS network
at a relatively easy spot like the headlight,
another bad guy will figure out how to
set the perfectly good Li batteries on fire with a BUS network command code.

I've been using a schumacher automatic with desulfator for years with no issues. Battery always out of car and cord plugged into gfci and isolated far away from flammables and battery sitting on concrete in open spot. Batteries are roatated as they peak out and sometimes charger is unpludded when everything is topped off. I check with load tester once a month or so and top off when under 12.v static and 10v under load.
Battery tenders are not regularly used and relegated to small out buildings housing tractors and lawn equipment.
Rechargable tools, name brand and only plugged in using the NON rapid charge charger only when I am home.
Fire alarms in all sructures repote buildings mounted near eave vents.
Most important. Anytime I'm away they are all unplugged.