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Here is a little smart battery charger with current limiting I made that works with the small gel cell type batteries. If you realy want to extend the life of your investment then after each time the battery is used, even only a little then it should be charged till the LED indicator goes out. After a set voltage is reached, the charging stops. I still have one of those heavy 8 amp-hour batteries, which is working well after 5 years of use.
After unit is built the max voltage needs to be adjusted for about 13.6V. This is done while the 20K resistor is removed and it's put it back in after. The 20K resistor is what lowers the voltage after a full charge is reached and if left in while adjusting you would be measuring the lower set point. The max charge current sense resistor has the familiar .6V drop across it so I=.6/R approximately. A 5.6 ohm is good for 2 to 4 amp- hour batteries, 2.2 ohms for up to 8 amp hours, and 1.1 ohms for 20 hour and up. I'll keep to an 8 amp or less for my bicycle though. A 1.8 ohm resistor works the best around here. Check back later for photos.