Having been through the pain of trying to understand my battery requirements as an off grid CC'er I thought I'd share my currwnt thoughts.
Battery life is adversely affected when there is no means to trickle charge them up to near 100% capacity after each cycle. Solar panels do help (mainly in the summer) but I doubt the batteries will ever get close to 100% if the batteries are used on a daily basis. Those who have access to a shore line each night are in a much better position to keep their batteries healthy for a long time as they can be trickle charged for long periods at low cost. Diesel and petrol is very expensive way to trickle charge and you can't easily do it overnight.
Find out what your daily power requirements are in amps. Someone here suggested I buy a clamp meter to measure the demand from the battery. It was very helpful in helping me check my estimated useage and voltage drops.
Try to find ways of reducing your battery demand. The whole exercise has resulted in us changing to LED lights and getting a 12v TV which runs on only 1.5 amps. We also have a gas fridge which reduces our electricity consumption by a lot but obviously costs more in gas! Our consumption is now around 15-20 amps per evening.
Once the power requirements are understood, choose the best battery to suit your needs. My current thoughts on this are that domestic batteries are more expensive than starter batteries and take longer to trickle charge them up to near 100% so are more likely to degrade quicker.
We are experimenting with a single 12v , 75 ah silver/calcium starter battery. Cost just under £100. So far it has met all our needs. It never drops below 12.3v (70% capacity) after an evenings use and charges back up to 13.0v (measured after 2 hours settling time) with 2-3 hours engine running per day. It also seems to handle heavier loads like pumps with less voltage drop.
I understand that starter batteries like to work between 70-100% capacity unlike deep cycle domestic batteries which are happier down to 50%. So I guess it's important to make sure they don't drop below this
As I say, it's all a bit of an experiment at the moment and it's early days. Even if this single 12v battery cops out after 2 years. It cheaper to buy another one than 4 new domestics (which is where I started from!).