Voltage Monitoring And Tending For Several Vehicles

I have several vehicles which I don't drive all the time. I often find a battery is dead when I go to drive a vehicle I haven't driven in a while. I have tried using the Battery Tender in my garage over a long 16ga charge lead to a connector (Anderson Powerpoles) hanging out of the hood. This works, but the human factor screws it up- ie, either I drive away without remembering to unplug (not usually a problem, as the powerpole is easily self-unplugged in this application) or the lead gets run over by the weedeater/lawnmower when the wife or kid decide to cut the grass. Honestly, there's an easy fix for that as well- but I'd rather have something standalone.... What I am looking for is something like a remote start, but without the remote. I want a system that will monitor the battery's voltage, and start when it gets to, say, 11 volts. I know there is a feature like that in the Bitwriter menu on DEI remote starts, but given issues with DEI having locked down their accounts about 10 years ago, I doubt I have the ability to just buy a BitWriter and do it myself. Plus, the local shops in this area... well, let's just say they don't fill me with a warm fuzzy feeling as to their employees. (This is totally on me, I am not accusing anyone of anything. But at the same time, I am aware that things do happen) Obviously the autostart feature of a remote start would be ideal. At the same time, I want the ability to disable the autostart feature entirely (say, maybe I am working under the hood, or I'm going to be out of town a while and don't want vehicles starting up unattended.. Plus, there's the obvious need to interface with an alarm in order to prevent it going off. I have even considered just installing a solar panel on the roof to keep the battery topped off. I haven't pulled numbers re: parasitic drain and charge capacity of a reasonable panel.... Surely I can't be the only nut that's ever thought of this? "Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"

I never used it, but I liked that feature on the Vipers. You can still DIY install them from online sellers. I do like the Bitwriter, too. Maybe you can find a voltage monitor with a low voltage alarm and use that to trigger a remote start.