I simply keep the battery connected and use a good battery maintainer in the off seasons. Note that with the Clocks4Classics repair method, they recommend keeping the clock running so that movement doesn’t become “stiff.”
Margaret, like the good dog she is, lives outdoors, no battery tender, Mike Eck-modified clock running 24/7.
Only ever failed to start once, and that was only due to an old battery.
Phil is more worried about electrical fires. Clock battery drain is negligible and much lower than on more modern cars. I disconnect after two weeks because I then have peace of mind and don’t have to worry about some fault developing (like interior lights switching on or the radio shorting itself out - and the clock does many beats on its small points so if I can spare it a month aka millions of ticks that can’t be so bad given that I‘m so happy that I can still hear it ticking).
My wiring is so good I‘m absolutely confident and my battery costs 80 USD so no worries about that at all.
Nothing wrong with using caution in disconnecting a battery, over time: my clock has no points, so that’s no longer an issue.
My main point is, in all my years of being around cars–thousands of them–not once did I ever see, hear of, or experience a fire caused by a battery in storage.
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Not unless you drop something metal across both of the contacts.
Never use the top of a car battery as a tool storage area when working under the hood,. . . or bonnet.
The clock in my ‘68 never worked. I set it at 10 minutes before two, just like in the Timex print ads. Apparently that’s the most pleasing analog clock position to the human eye and brain, according to Madison Avenue at least. When I retrofitted (retrograded?) the toggle switch centre dash I put the rocker switch centre dash, along with the non functioning clock, in The Box™ along with all the other S1.5 stuff I’ve either removed or replaced over the decades. Now there’s no clock in my E-type, functioning or otherwise, and I don’t miss it at all. So, when I’m out driving it’s a genuinely timeless experience 
.
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Speaking from experience?
Anyway, dropping something across the posts, disconnected or not, will result in a 3/8ths inch Snap-On extension becoming a slo-blo fuse
Don’t ask.
Not personal. A friend of mine told me he saw a battery explode when someone set a wrench on a battery while working on a car. This was maybe 50 years ago.
I had one explode, as I hooked up a charger: removing a cable end would make little difference, in preventing a boneheaded-caused 'splosion.
Never have the + pole exposed and it can’t happen…
I put tools on there but only if it’s impossible for them to short the battery.
My clock was disconnected for many decades and runs well. I had to speed it up after a hail storm after which there was not one dry area left. After a few weeks I had to slow it down again; I don’t think they suffer much if not running for a period, at least not more than by running.
What kills them and that was an issue back in the day is not starting them, because if you’re unlucky the contacts burn up and that is probably what happens happened in most of them. 10 past 10 is what I set my clocks to.
And nope, a stationary car shouldn’t catch fire, but many feel better that way and after all this is the time the cars are not under supervision - but then the time is not watched doesn’t really matter doesn’t it…
Upgraded, there fixed it for yah.
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Two instances;
Elder brother using a battery as a source for welding back in the 60’70’s must have been too close to the arc and the gasses exploded.
Not the battery this time but had the sons Mini clubman in the workshop, was about to go home and happened to look across at where it was sitting, fire! Under the drivers seat, the son had bolted in a different seat and used a large square washer on the underside, this was squashing the main battery cable and it shorted out.
10 mins later and I would have been on my way home and looking at an insurance claim in the morning.
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A mechanic working at a local garage which does quite a lot of work on classic cars left a spanner on a sloping panel near the battery and went home.
Now they need a new garage.