Hello Bill,
How big is your small stream? The 5 foot head is not bad for m-amp battery charging even if you use a small plastic pump sized to your gallon/per minute flow, although those pumps are not efficient. You would probably be better off using a squirrel air fan driving a stepper motor (see:
http://www.thebackshed.com/windmill/
coming close to a crossflow turbine if you don't want to go through the effort building a proper crossflow turbine for your stream, see my Webpage:
http://www.fight-4-truth.com/Alternative%20Energy%20Page.html.
It just depends how much effort you are willing to spend.
I use a fencer myself running it at night against bears and deer, shutting it off in the morning to charge my one dollar 12V deep cycle battery with a dinky 10 x 14" solar panel, which works like a hot dang. Watch the ground rod/cop.tube, it must be in wet ground. Install the fencing wires alternatively, hot, ground, hot, ground, which is very effective on dry soil especially. See my other page just above INDEX NO. 5--- text about my one dollar battery:
http://www.fight-4-truth.com/Parts%20Page.html
You can not draw current from a battery while under load and keep your battery alive, which is the reason car batteries do not last, hence in your daylight case you would use two batteries while the one is running the fencer the other is charged with solar power using a double through switch.
In the other hand if you like challenges, then build yourself a small Bedini battery charger which, runs itself off of a 30.00 dollar (CA) garden tractor battery and forget the hydro problem. It will charge its own battery and also charge your fencer battery. Again thumb through my WebPages, the info is all for free:
http://www.fight-4-truth.com/Work%20Shop.html
http://www.fight-4-truth.com/Schematics.html INDEX: oo Monopole magneto 11a
Cheerio,