Well, I have a 12V 9AH SLA Battery, and I use a 7815 + a diode in series to charge it, (I really wanted to build a charger using the L200 or the LM317 but I couldn't find any of those in my city). So, I've read "Battery University" and I ended up with more questions than before.
First, It states that the open circuit voltage of a fully charged battery is 12.65V however, mine came with an open voltage of 12.93V, (And the delivery took a whole month) was it overcharged or is it its real 100% charged open circuit voltage?
Also, I've read that the battery shouldn't reach more than 14.4V to prevent gassing, however mine even without the diode (I know it is risky without the diode if I unplug the charger) doesn't get close to that voltage, after hours of intentional "overcharge" the highest voltage that I could reach was 13.5V and it didn't go any higher. then after unplugging the charger and waited a couple of hours, I measured its open circuit voltage, which was 13V. (Which seems to be the real 100% charged voltage of this battery, as it measured 12.93V out of the box after who knows the last time that it was charged).
Also, when it is charging I wait until the current drops to 2% of its amp-hour capacity, however if I wait an hour and try to charge it again, the current jumps to 0.7 amps and stays that way for hours until it again settles down to 2%, it seems that it could keep doing that forever.
(By the way battery university states 3%, while "Lee Hart's Battery Charging Basics" states 2%, who is right? xd)
Am I destroying the battery? My meter measures temperature and the battery temp always stayed at ambient temp, even when "overcharging" it.
And finally, what is the float current of the battery? Because I want to float charge it by simply adding a resistor in series to the charger, instead of adding a bunch of diodes in series to reduce the voltage.
Right now I treat it as an old battery (even though it supposedly isn't), I wait until the current stops falling (which happens really close to 2%) and I unplug the battery, however, shouldn't an old battery open voltage be 12.9-13V?