I believe that you are worrying about nothing. The car should be able to easily sit without a charger on it for a couple weeks at least and still fire right up. If it will not then you either have a bad battery or some type of parasitic load draining the battery. It is entirely possible that since you always have it on the charger that has ruined the battery batteries need to be exercised (draw, charge, draw charge, etc.). Before I go in to this further I should point out that a Model A can be push started quite easily, it also can be jump started even if its still 6 volt as longer as you don’t have electronic ignition and you don’t have the lights on while the jumper cables are on. I would let the car sit overnight without a charger on and see what happens, the 2 days, etc. If the battery wont start the car then charge it up and disconnect the battery cable for a couple days and then try it, if it starts then look for what is draining the battery. I’m not going to write a book about how to look for the drain but there is not much to go wrong on a model A so it’s not difficult. Before a thousand people jump in here I will point out that the battery should be disconnected when the car is parked anyway. I prefer a switch that disconnects one of the two battery cables (either one will work and it’s actually better to disconnect the ground side (Pos. If still 6 volt Pos. Ground, and Neg. if it has been converted to 12 volt neg ground) or, at a bare minimum install (if you have not already) a fuse in the wire that leads to the junction box from the starter cable post and remove the fuse whenever the car is parked. On the flip side, if the battery still craps out when the cable is disconnected then you have a bad battery. A battery that is not used at least every few days cannot really be counted on after 3 years regardless of what battery you may buy. After that, you are on borrowed time and it’s up to you weather you just replace it at 3 years (which is what I do) or continue using it until you get stranded some day. A battery that is on borrowed time may start the car if everything is good but them some day you forget to turn the ignition on or turn the gas on or it’s particularly cold out, etc. and the battery is called upon to provide more cranking power than usual and it can’t do it. Read and digest all this and then if you need more info. Also, I could mention that a Model A can be crank started in a pinch or you can just carry one of those inexpensive little jump packs like you can buy everywhere these days. For those of you that feel you should jump in here comments you feel you just have to make, and bury Kent with detail etc. etc. I will say that I have been a marine, commercial, industrial electrician for more than 50 years and I do know what I am talking about.