sewin, you struck a cord with me in relaying your real world experiences with digital tec. Being somewhat of a Luddite, I do indeed become rather frustrated with the ability which digital control functions really require that we humans adopt procedures to fit their requirements in ways that may be logical to the programmers as long as we operate to their imagined norms...?
i.e. vehicle designs are such that they are expected to be in at least semi regular use, thus the battery is again expected to maintain enough charge and discharge cycles in order to function as us humans might expect...even in terms of longevity, with the battery showing expected issues as it ages and may require replacement...?
However, in the case of digitally controlled vehicles which may be subjected to irregular use, or even stored for months on end, it seems they have not quite got around to a system whereby even in sleep mode there may be still a measure of drain on the battery, though I suspect the issue of lack of use/storage, if not on a Ctek or similar, may well be exacerbated by the wakeup demands placed on the battery that may not seem entirely obvious, and given the load placed on a battery that has suffered parasitic draining over a period of time, these wake up demands might just be the straw that brakes the camels back, even before the starter is finally engaged ...? If one adds not only the age of the battery, but also the duty cycle it may have suffered over time, then is there any wonder that it might fail to fire up the engine...?
Also in regard to choice of Ctek/float chargers, might be best to be sure to buy one that suits the type of battery, be it old style lead acid, Gell battery of AGM construction, or I think there are even newer style batteries of different internal construction that may require a charger/charging regime relative to the needs of their chemical makeup.... Though pretty sure Ctek and others will be up to speed..
BTW just to present another real world view..... The battery on my mid 80`s +8 used to drain down in time as the result of it not being even semi regularly used (blame a self build project) the cause of the drain down was the small but constant load of the immobiliser system. The purchase of a basic Ctek MXS 3.6 put an end to the battery issues other than those age related.. I also have a car with an AGM battery and it is kept maintained by a Ctek MXS 5.0 which has a specific AGM function.
.As ever, more than happy to be corrected if anything I typed may be considered incorrect..
