batteries - should these cost the earth?

I think you have set your expectations a little too high...

Batteries CAN last a long time (and by that I mean 10 years or so) but they will not have the same capacity as when they were new.

I think you should expect a set of GOOD batteries to last 5 years. If you get more than this, then smile because you are doing well. If you abuse them by overdischarging, overcharging, or not topping them up then they will last considerably less than this.

The only real way of knowing when your batteries are on their last legs is when they fail to hold charge as well as they used to. This is very subjective as they degrade from day 1 but the degradation curve gets steeper to the point that you actually notice it. Sure, there are certain tests such as SG of the electrolyte, and standard discharge tests but I do not think they are as good a judge as your own observations.

There are oodles of battery suppliers and I cannot say whether one is better than the other. The method of constructing a battery is messy, agricultural, and low tech. There have been some advances in battery construction and the addition of trace elements to enhance performance in specified circumstances but the basics have stayed the same.

In my experience, there is no substitute for lead. Lead is heavy and therefore the weight of the battery is a pretty good guide as to its capability. However, weight will not determine its longevity. What does determine longevity is how you treat it.

This is how I would go about it (but recognise that I tend to overengineer things so that there is a significant margin and therefore less likely to let me down...)

1. Determine what size of battery bank you require (say 1000 Ahr), then double it as a minimum and maybe even treble it.
2. Buy "deep cycle" batteries. If the supplier is offering a 3 year guarantee then it is probably a good battery. If the guarantee is less than 3 years, then expect to pay less proportionate to the length oif guarantee.
3. Find out what the maximum charge and discharge rates are for the batteries you have spoecified. Organise your charging such that you never exceed HALF the rated amount.
4. Similarly, your battery bank should be sized such that you never exceed HALF the maximum discharge rate that your system will load the battery set.
5. Make sure that the batteries NEVER get to see temperatures of less than -(minus) 5 degrees, and +30 degrees.
6. Inspect your batteries every week and top up the ones that require it.
7. At the first sign of a battery failing - fix it, or at the very least isolate it from your set. Signs of failing are excessive gassing, excessive corrosion of the terminals, or excessive topping up required.
8. At the first sign of electrolyte leakage, isolate the battery and remove it.
9. Plan to replace ALL the batteries after 5 years. NEVER replace an old battery in the set with a new one - unless you plan to also replace the new one when you repalce all the rest in the near future.

Some people swear by gel electrolyte batteries but they are less good at giving you performance feedback as you cannot see what is happening. Liquid electrolyte cells allow you see if the plates have buckled signifcantly, check sg, check levels, see gassing, etc so you get a little more warning of an issue.

Most people would regard a lead acid accumulator as being environmentally unfriendly. Lead is toxic and it is lead that makes the battery work. Having said that, nearly all areas and most battery manufacturers now have schemes in place to recycle old batteries - even to the extent of paying you a small fee for the old ones.

I hope this helps.

regards,
Ian