BigJimny has dual batteries fitted. A slightly enhanced standard battery for starting and a large battery in the boot for the winch. Having just replaced the batteries when rebuilding BigJimny, I decided to put a monitor in. A quick google showed a number of expensive systems but also a new cheap system from the Chinese discount sites.
I picked up one from Amazon on the basis that, although cheap, Amazon would refund if there was any issues. I purchased one of these DUAL BATTERY MONITORS for the princely sum of £13.49It is designed to be a "standard" sized switch. Now Jimnys do not have standard switches, the Jimny standard switches are slightly smaller. However I have a home made switch panel that take standard sized switches so I can fit it there. I did measure up the Jimny switch panel (the one on the upper right of the dash on the drivers side) and it does look as if it could e fitted in here if you were happy with a slightly protrubing fit.
It turned up within a few days and looks to be a well made unit. It has two battery inputs and an earth terminal. I connected it up and noticed that it did not have any sort of internal switch, no matter which voltage input is connected, it turns on. Therefore it cannot be left connected to either battery otherwise it will run permanently and flatten the battery.
The only way to operate it is either to switch the feed from both batteries or switch the earth pin. I decided to switch the earth so I connected it through a ignition relay I had and it works fine.
The pictures above show it in place (the switch panel is looking a bit weary after a few years of being kicked and covered in mud). In the first you can see it with the engine not running but with the main battery running the lights etc. In the last picture the engine is running and the alternator is charging.
The display is a bit over-exposed by the camera, it looks great in real life.
I am very pleased with the results for less than £15.