I was riding through the local college campus via the MUP and this guy noticed the circuit board connected to my bottle dynamo and wanted to know all about it. I described the LM-317 regulator circuit shown in this thread. He tells me he's working an electrical degree and said I didn't need the regulator or the capacitor. All I needed were two NiMH rechargeable batteries across the bridge rectifier to regulate both the voltage and current for my 2 AA flashlight and 5,000 MCD taillight. When I got home I tested his design and he was correct! I subsequently tried a 3-battery setup with a 3 battery LED light and the 3 batteries regulated the voltage and current perfectly as well. I subsequently have built the circuit and have been testing it. It's great! I did 30 miles and my lights never went out at any stops and I even walked my bike up the very steep hill home with both the flashlight and taillight working fine. I've even ridden around with the switch open recharging the batteries as I ride. At no time can the dynamo put more than 500mA across them or exceed the voltage required for recharging them. I tested the current for the LED's and found that he was correct. The LED's take what they need and the batteries sink the excess current for recharging them. It's doesn't get any better than this!
I've found that the dynamo starts recharging the batteries at 8 MPH with the LED's turned on. With dead batteries the LED's will illuminate at 5 MPH. I started a test run with dead batteries just to make sure the LED's would still work with discharged batteries and they work exactly the same as the LM317 regulator circuit with no batteries.
Here is the circuit and short information he made for me.