Hey, just thought my first post would be reviving and old thread
But since some of the subforums don't get much traffic, maybe this doesn't count as an old thread?
For anyone building solar where you don't don't need to use the battery in freezing weather (or can protect the battery from freezing), I strongly recommend you take a look at LiFeP04 batteries. They're lithium, but not the lithium-ion type in your laptop.
A lead acid (flooded, gel, agm, etc) will probably last you around 300-500 charge cycles if you only disharge it around 50%. A LiFePO4 battery should last over 4,000 cycles with a 100% discharge. The downside is you can't charge them below freezing without damaging them. If you can manage the freeze issue, you get a much lower total cost of ownership over the life of the battery with only a minor increase in cost for a given usable capacity.
For example, a quality 100AH lead acid battery probably costs around $100-$150, with a usable capacity of around 50AH. So it would take 2 to get 100 AH usable. A 100AH LiFePO4 runs $300-$350 on amazon. So its close to the same upfront cost for the same usable capacity and it will last thousands of cycles. Plus higher charge and discharge rates (typically 1C, which means a 100AH battery can safely sustain 100 amps charging or discharging).
Just be careful of some cheap batteries on Amazon falsely claiming to have low temp protection.
