I bought a voltmeter instead of an ammeter. I wanted to know what is left. It was about $3.50 from Bangood in China.
Connected it up to my positive and negative, and it tells me to two decimal points how much battery capacity I have left. It uses a ton of power to run it though... I think about 1/10 of an amphour in a month.
It's just set in place behind the cover panel on the breaker box, I open the lid, and check out what's left. Very nice indeed to know if and when I really need to charge, and to know how much is being used daily.