Since I primarily build large robots, I have always had issues with power control, charging, & extending battery life. I use large gell cells and it seems like I was always either over-charging them or not charging them often enough and they would die prematurely.
It occurred to me last night that instead of trying to design & build my own power controller, (which I've always done in the past), that the answer to my problem might be as simple as an off-the-shelf unit designed for solar power systems.
I searched Ebay today and found this 12/24 volt unit for $6.50 with free S/H.
http://www.ebay.com/itm/262020348616?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Since I couldn't begin to design & build a unit with similar specs for that price, I ordered 2. If you think about it, it does everything you need for power control:
It takes in an unregulated DC and PWM conditions it based on battery state of charge.
It controls the output power, correcting for over / under voltage and providing for "Low Voltage Dropout" so you don't over-discharge your batteries.
It gives a visual status indication of what is going on.
The pass-through voltage drop is only .12 volts.
It also employs over-temp protection.
That's a lot of features for $6.50 and if it simplifies my design and extends the life of my expensive gell cell batteries in the process, it's a win / win.
I will post a follow up once I receive them & try them out.