Batteries work by moving ions across a barrier via a chemical reaction. They need to be kept warm (roughly 10 to 25 degrees C, or broadly speaking, room temperature) and dry. The colder the battery is, the longer it'll take to charge, just like a car battery in the dead of winter. As with anything involving electronics, avoid extremes in temperatures; they can cause breakdowns in the chemical reactions that run your batteries. Since you're probably building your own battery enclosure, spending the money on high quality insulation is a good idea. Never let your batteries freeze.
You'll need to regularly monitor the storage capacity of your batteries, to know when to maintain them. Good battery care habits can more than triple the life of your battery system. You'll need a volt meter and hydrometer to do this; the first tells you how much voltage you're getting out of the battery, the second tells you the status of the electrolytes in the battery itself.
Your batteries are going to consume water; make sure that you fill them with distilled water to keep them running smoothly. You'll want to keep your batteries at a 50% charge state to maximize battery life, and you should keep your batteries electrolyte levels at the indicated level.
Because batteries run off of a chemical reaction, when they're charged, they can emit hydrogen and free oxygen. Keep your batteries in a well ventilated space, an away from open flames. Oxygen, in particular, is a primary source for contact corrosion. You'll want to inspect your battery contacts about once every six to eight months and clean off corrosion. Putting a layer of grease on the contacts will keep them from corroding as quickly.
As part of your maintenance progress, you should check your batteries for signs of aging. As they age, batteries get less efficient. If they're hooked up in parallel, their capacity drops. If they're hooked up in series, their voltage drops. Roughly the same time you check the contacts for corrosion and apply a new layer of grease to them, you should be running a capacitance meter and volt meter to them to check their overall performance.