It's not a jimny so I need help.

As an owner of 3 classic cars that get used infrequently I wouldn't expect the battery to remain healthy between use without the aid of a trickle charger of some form. These vehicles are old school, with no parasitic loads or a very low load, radio memory etc. The alternator's aren't smart, stuffing over 14v and as many amps it will take into the battery. Even on these, 4 starts a year without battery assistance would be pushing my luck.

No agreeing with your dealer, but modern cars have a higher parasitics loads and you are at the mercy of the " smart alternator map" however that's written. You also have natural battery discharge which everyone forgets, this increases with battery age and it's construction. I would have to go down the logging route, recording the parasitic load over a few days and doing some rough calculations based on this / battery capacity/ natural discharge to see if the Land cruiser has issues. But as we speak today my logging DVM is bust and the software won't run on windows 10, so it's no longer an option.

So I would just fit an external smart charger ( Aldi etc) or a window solar panel to it and go for a drive in the Jimny. If you go solar get one above 6W, the low power ones don't work well in the UK, not enough sun

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Can you disconnect the battery earth lead?  Depends in the risk of theft where you live (no alarm).

My gen 4 stood for a month and it's battery was completely drained. The only parasitic thing above standard is national luna battery monitor.

I have had a lifetime's experience of a flat/draining battery on my Boxster. For the first 8 years of my ownership it eat a 75-80Ahr battery in about 18 months, didn't matter what battery I would buy it would go through them.

Boxsters have a reputation for a high current draw when they are sitting there doing nothing and after a week it switches the remote central locking off to save power, that doesn't work. It will flatten a fully charged battery in about 5 weeks, just stood there. The Jimny is pretty much the same.

I bought a solar panel (for both cars), as Martin says get a big one, mine are mono-crystaline 20W panels and still don't really maintain the charge, but do help.

I also bought a Ctek MXS 5.0, that helped bring the charge up after the car has stood for 2 or 3 weeks without use.

After years of struggling with my Boxster I finally found out what was the main problem, the alternator started to go and was clearly faulty for some time because when it had a new alternator and then another new battery, that one lasted for around 4 years and was replaced in the early days of Covid and is still going strong nearly 4 years later.

I also bought a battery tester, Ancel BA201, it shows state of charge (just voltage really), but measures starting current (CCA), alternator charging and ripple, they are very useful. I don't use it much but tested a neighbours battery and alternator the last week, he was having starting problems, his battery was a bit down (50% charge) but the CCA was only half it's quoted value. He borrowed my Ctek and after a full charge his car is now fine.

The other thing I did on both my Boxster and Jimny was to measure current draw with the car locked and no lights on. You can do it with a multimeter on a current scale by inserting in line with the battery lead (don't try to start the car). My Jimny measured about 50mA after everything had switched off. I am lucky I also have a DC current clamp, so don't need to disconnect anything, but these are a bit expensive for every day DIY use.

50mA per hour is 1.2Ahr per day, you can see how the Jimny battery at 45Ahr will discharge in just over a month. My Boxster was significantly more than that, about 1A for 30 mins after you lock it, then falling back to around 150mA for a few hours before dropping a bit. No wonder it flattens it's battery.

Not been funny and you might not want to say, but do you lock your Land Cruiser, if not it will draw a lot more current and it gets even worse if you leave the keys in the ignition, but not switch on.

I would suggest measuring the current consumption with it unlocked (no lights on) and then locked. If the current is high, check it on the forums and see if it is normal.

If it is normal, then Roger's suggestion of disconnecting the battery, or pulling the main fuse is the only way, unless you want to trickle charge with a Ctek, it's what I used to do with my Boxster when I wasn't using it for a few weeks.

Robin

Good luck with the dealer. Unless it is an easy fix they will do whatever is quickest/cheapest for them and if they don't employ an auto electrician it will be a trickle charger.

Robin

Using a vehicle only 4 times a year is not what it was designed for, so accept that it will do the things that you don't want it to do and sneak round the corner and out flank it ie fit a C-tek or similar and leave it permanently on charge.

Roger