Lead Acid Battery Charge C/20Ah

Battery University is a good starting point. A vast amount here Battery University

Particularly:

Charging Lead Acid

Based on the following, it would SOUND wise to charge fully for "a while" under trickle and then to open circuit the charger until Vbattery fell to approaching 2.1V/cell. A controller to implement this could be extremely simple.

Dangerous in isolation, but, they say:

• Most stationary batteries are kept on float charge. To reduce stress, the so-called hysteresis charge disconnects the float current when the battery is full. As the terminal voltage drops due to self-discharge, an occasional topping charge replenishes the lost energy. In essence, the battery is only “borrowed” from time to time for brief moments. This mode works well for installations that do not draw a load when on standby.

  Lead acid batteries must always be stored in a charged state. A topping charge should be applied every six months to prevent the voltage from dropping below 2.10V/cell. With AGM, these requirements can be somewhat relaxed.

  Measuring the open circuit voltage (OCV) while in storage provides a reliable indication as to the state-of-charge of the battery. A voltage of 2.10V at room temperature reveals a charge of about 90 percent. Such a battery is in good condition and needs only a brief full charge prior to use. If the voltage drops below 2.10V, the battery must be charged to prevent sulfation.

  Observe the storage temperature when measuring the open circuit voltage. A cool battery lowers the voltage slightly and a warm one increases it. Using OCV to estimate state-of-charge works best when the battery has rested for a few hours, because a charge or discharge agitates the battery and distorts the voltage.

From everything I've seen so far with lead-acid batteries, a CV charger may not be ideal, but as long as you aren't hydrolyzing the acid (apparently at 14.4V), it'll charge itself over time. You'll likely hit the current limit on the turbine initially before current tapers off, so I guess you do sort of have a constant current source initially. The only problem is that you mention the generator provides ~100mA, which is small for a lead-acid battery... If your discharge rate is lower, I suppose it would charge. Keep in mind that certain batteries (ex. deep cycle) are better suited to this type of application.

Hopefully this helps, but feel free to request clarification if I missed something.