The 12Vbatter charger circuit uses a TL431 voltage detector and a TL431 constant current source. RU-vid video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-k1TOiKuBBG8.html www.bristolwatch.com/ccs/tl431_ccs4.htm TL431, LM317 Battery Charger Circuits Schematics