I See Electromagnetic Fields!
-- But, I am still not 100% clear on what voltage = a 50% charge in a standard 12.6 volt SLA battery? One calculation example led me to 12.15 volts as a 50% SOC on an SLA battery. Is that correct, so I can watch it carefully?
Here's a manual for one brand AGM. Page 35 has voltage vs. SoC