I might use a power Nfet with 5Khz PWM to pulse charge lead acid batts. The 12V batts may be as low as 3 V to start with. Batts with voltage that low will have an Int Resistance of upwards of .1 ohm, dropping to under .01 ohm at max charge (around 13.2v)0
As I want to use a .01 ohm current sense resistor to control the PWM I need avg current as opposed to sampling the spikes, therefore the 15KuF cap may have to come after the NFet switching (in parallel with the batt). The adc will be fed by a Diff. op amp, both ref'd to a lm4040 4.096v precision source.
Lead acid batts. act like huge caps., so I am not sure if the 15Kuf Cap is really necessary to smooth the current flow to measure with the current sense resistor.