Yep, total PITA. This thread
will tell you more than you ever want to know about tank monitor theory, but the end result worked in my Overlander.
An improved digital version, with better battery monitoring and some added temperature monitoring, is taking shape in this thread
...I'm hoping to upgrade to multiple batteries & a generator/solar system in the next few months.
I'd like to throw out a small caution about multiple batteries. Unless you have a very specific requirement for a known volt-amp capacity, stick with one battery--no matter how many batteries you add, you'll always need a little bit more juice now and then, which puts you right back in the same position as you were with one battery. Except you're a lot heavier. IMHO, if you have a generator, you'll find that you can easily boondock for three or more days on one battery and in that time you can find an acceptable time to recharge with the generator. Solar puts you in even better shape, maybe never needing the generator except to run the microwave.
I tried two batteries in my Caravel
, which allowed me to boondock for a week, but I never added a 2000W inverter (a bad idea IMHO--you're talking 70-85 amps at 12V
for even modest 115V appliances), so a microwave (or hair dryer) was out of the question. The Honda 2000I quiet generator solved all my power problems (some of the $50 microwaves can't hack the initial voltage dip when they start up using a small generator--you sort of have to hand-select the right one).