The biggest problem is that for directional lights to work the batteries need to be near or close to The maximum voltage of the light. If the battery voltage drops (and the voltage DOES drop as the battery losses power) the directional blinker stops blinking. This occurs WAY before the battery is done as a power source for the light. My guess is when the battery has used about 20% of its power, the voltage has dropped so much that the blinkers stop working. You then have to get new batteries or recharge the old ones AT LEAST FIVE TIME BEFORE you have to do to the light no longer working as a light. The main reason for this is Indicator Lights uses Voltage as the mechanism to Blink, unlike blinking lights that just restricts the electrical power to the light. Voltage is used for then you can use the light as a light in addition to a turn indicator (You then use voltage to blink the light when it is otherwise on as a tail light). The better solution would be a separate indicator light from a tail light but I have not seen such an indicator light.
Some sites for Blinkers:
I have never tried this one, but looks god from what i can tell:
http://www.global-merchants.com/home/bike.htmI have used this one, but it does NOT come as a complete light you have to make it yourself with parts provided by the maker of the light. I have shorted the battery several times, but when it was working it was VERY bright. The problem is mounting the Battery, you have to be careful NOT to short out the battery for it is a 6 volt Emergency light battery.:
http://brakelite.com/I Just found this this one out of Australia, I have never tied it, but all it is a a light on your hand, works off of motion of your arm.
http://www.safeturn.com/reviews.htmlI did try another company, which I can not find at present, while I liked its switch, its connection between the light and attachment to the bike would break making the whole thing unusable.