The problem with using conventional diodes is there voltage drop. Standard silicone diodes drop 0.6 volts and even Schottky diodes drop 0.3V so the batteries never receive a full charge, also if you put a diode in each leg as you suggest then the
solar controller looses its power supply when over night ( no
solar and no feed from the batteries) and depending on your controller it can reset itself.
For the DIY electronics enthusiast I can recommend this little device which I came up with myself.
View attachment 118821View attachment 118822View attachment 118823
It's very simple and consists of a smart bypass diode SM7461 in series with a 12v 200W halogen lamp.
It's fitted between the 2 batteries just like any other
battery maintainer but has several advantages.
1, It has NO voltage drop, the cab
battery is held at exactly the same voltage as the hab
battery.
2, It requires just 2 connections, no neg connection is required.
3, It's extremely efficient and consumes virtually no power in it's self.
4 It can be left connected and doesn't need to be removed when starting like the simple
fuse link a la Clive circuit.
5 it's cheap, parts cost less than £15.
The 200W 12v halogen lamp is made up of 4X50W capsule lamps. The pics above are of one I built and used before I moved to a B2B. Worked perfectly.
The halogens fit nicely into a small.piece of perf board, remember to beef up the tracks with solder cos of the current. The diode doesn't need heat sinking because it dissipates virtually no power because it's either hard on ( ohh er missus) or off.
The lamps act as a very low ohm PTC thermistor, (they never light up) and protect the device/wiring in the event of cranking the engine with a flat cab
battery and a full hab
battery. You're probably best to add a 5A
fuse in series with the device.
Merl