My truck would sit for weeks, and the battery would go flat.  You know, flattery of the battery.  So, I'd have to take the battery out, drag it upstairs (my parking is in a basement garage in my building), scrounge up a battery charger, charge it, and reverse the process.  Again and again.  The breakthrough came when I became aware that there was an electrical outlet in the garage.  Time to get serious.  I thoroughly studied Amazon's website for an appropriate charger, and decided on this little beauty.  It is designed to be permanently mounted in a vehicle (such as a hobby car that's rarely driven), or a boat, or a riding lawn mower, or you know whatever.  It is permanently wired to the battery, and merely plugged into to go to work.  It has a little computer which knows what to do, so it'll charge the battery, then switch to maintenance mode to sustain the charge, and it communicates it's behavior and the battery state of charge through LED lamps.  I installed this unit in my engine compartment, bolted to an inner fender panel, and indeed permanently wired it to my battery.  I don.t leave it perpetually active, but when the battery charge wanes, I just unreel an extension cord, plug it in, and in a few hours it's charged, and the LEDs tell me so.  This unit, so installed and so used, has completely gotten me off the hook for the flat battery travail.  It's quiet, it runs cool, and it does the job.  Honest, it's doubled the joy of the vehicle.  This story emphasizes one of the chief secondary merits of Amazon, which is research on their website, which is a wonder of practical  information.