The idea of this project is to be able to monitor the leisure batteries in my motorhome. These batteries run things like the fridge, lighting, water pump, etc in the van. It also supplies power to the heater (a diesel-fired Webasto Thermotop) for the water pump, glow plug etc.
There are 3 x 115 Ah leisure batteries connected in parallel giving me a 345Ah 12V battery bank. This is charged by either a 64W solar panel on the roof and/or a 50A Sterling Battery to Battery charger that charges the batteries when the engine is running.
So first to mention, lead acid batteries are pretty much the oldest form of battery type and have stood the test of time well. They are fairly robust (compared to battery chemistries like Lithium Polymer), and fairly forgiving of abuse. That said there is accepted best practise with them, and by using them properly you can extend their life and performance significantly.
Dealing with Lead Acid batteries though is quite a complex issue when you get under the covers. Trying to answer seemingly simple questions such as 'how much charge do I have left?' or 'How much longer until my batteries are empty?' are actually very complex and dependant on a number of factors such as temperature and current load on the batteries.
I am *not* an expert in this, and don't profess to be. I've done a fair bit of reading on the subject and do think I know what I'm talking about, but please feel free to correct me at any point! I'm also not aiming to get a 100% accurate answer. I want an answer that is 'good enough' but at the same time I want a reasonable confidence that the answer is fairly accurate.