Below is a lead acid battery charger schematic using the famous IC LM 317. The circuit provides the correct voltage to charge the 12v sealed lead acid batteries or 12v SLA batteries. The charging current can be adjust with 1k potentiometer. This sealed lead acid battery charger circuit is automatic
automatic so you don't have to pay attention on the battery to full charge because the circuit automatically shift its function to trickle charge when the battery become full charge. Connect the battery which you want to charge in series with a meter and adjust potentionmeter to get the desired charging current. Use a good heat sink with IC, the input current should be minimum 15V to get 12V output to charge the battery.