So I am trying to charge a 12V 1.3Ah lead-acid battery(actually they are two 6V batteries in series). Now I have a power supply which says 12V 500mA but actually outputs more like 21V.. No idea why.. So I looked up how to charge a lead acid battery and saw that most people recommend a buck-converter like the XL4015, which can be used to control current as well as voltage. But I just can't seem to find XL4015 anywhere near I live. All I could find is LM2596, which only lets you control the Voltage and not the current.

Now I read that batteries should be charged at around ~30% of capacity, so that for me would be .3 * 1.3 = .39 A ~ 400mA. However the buck converter LM2596 will actually supply more like 600-700 mA. What is an easy way to control the current in this circuit? I am not really concerned about efficiency, so I would be fine with using a resistor, assuming it's easily obtainable...

  • \$\begingroup\$ you seem to be piecing together information, mainly from discussion forums and the like. THat really isn't a good way to understand what you need to be doing in order to do it right: You might really want to look into an application note of a semiconductor manufacturer on battery charging. \$\endgroup\$ – Marcus Müller Feb 14 at 13:08

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