I need electronic guidance...

[Rawze]

a couple 50-amp power diodes in parrellel mounted to a small aluminum plate for heat dissipation (isolated from ground). The output of that into an old-school style car brake-light bulb (single element, not dual) mounted on a socket (also isolated from ground). the output of the car bulb into the hot sid of the battery. No component(s) should be grounded, only tied to the hot side. When the battery wants to draw a ton of current because it is low or dead, the tail light bulb will light and limit the current nicely to about 8 amps or so. The doide(s) will only allow the power to flow towards the battery, the light bulb will prevent shorts and limit current. When the bulb is lit bright, the battery is very low and when the light is out completely, the battery is at full charge. You also need a fuse for fire prevention.


--> Power source lead --> 15-amp fuse --> couple over-sized diode(s) in parallel --> lt.bulb in series --> hot side of battery.

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Just some thoughts that come to mind. Maybe there are better things but I have made a few isolated trickle charge battery boxes like that over the years.