Brian:
One option I have not seen mentioned in this thread are golf cart batteries. These are one of the most popular options for budget conscious energy storage applications. They strike a pretty good balance between cost, durability, etc. I believe they are typically 6 volt cells. You can combine them in series to up the voltage (e.g. 2 batteries for 12 volts, etc.).
When I was implementing my solar array a couple of years ago, I spent quite a bit of time studying batteries, charging, etc. As someone already mentioned, www.wholesalesolar.com carries a variety of batteries and also has many good articles on charging systems, battery maintenance, etc. This is where I ended up buying my solar panels and batteries.
Anyway, when I was on that project, I was surprised to learn that the batteries are actually the largest cost item in most alternative energy schemes, such as solar. In my case, the cost of the batteries exceeded the cost of the solar panels by some bit.
In the end, I decided to go with some Rolls batteries ( www.rollsbattery.com ). These batteries are kind of the “gold standard” when it comes to energy storage. Unfortunately, they have a price-tag to match. I decided to go with AGM batteries because I had a mobile application with the batteries inside my camper. So, I didn’t want to deal with the hydrogen venting (AGM’s can still vent to some degree, but not nearly as much as conventional lead acid). However, it is my understanding that the conventional lead acid batteries are somewhat more cost efficient.
On the subject of charging, you are correct that there are multiple stages to charging (bulk charge, etc.). The more expensive your battery bank, the more care you want to exercise in making sure that you get a charger which matches the desired charging profile of your batteries, because mis-charging is probably the 2nd most common problem which leads to shorter battery life. If you are using cheap batteries, I wouldn’t sweat it as much. But if you are using expensive batteries, I would study the manufacturers recommendations, and make sure that I got a charger which matched the desired profile. In my case, I used a programmable MPPT charge controller from Midnight Solar.
The most common source of battery failure is excessively depleting the batteries, and/or letting them sit around in an uncharged state. You generally do not want to discharge deep cycle batteries below 50% capacity. Many inverter/chargers have a programmable disconnect which will stop drawing on the batteries when they reach a certain level of charge. However, I was surprised to learn that in my application (which involved mostly DC loads), there was no simple “off the shelf” solution to prevent the batteries from being excessively discharged. I eventually found a battery monitor designed for marine applications which would track the level of charge in the batteries with great accuracy, which had outputs designed to trip a disconnect relay. I designed a disconnect system around that. It would reliably disconnect my batteries whenever the charge dropped below 50%. However, I also designed in an over-ride function so that, in a bonaafide “emergency” I could fully deplete the batteries if necessary.
