@aricohelo sure it can be done. all you need to recognize is that the Lead-acid batteries charge different. Those batteries have three different charging stages on which one of them requires an overvoltage. Hence your power supply being a 18V supply. To convert your equipment, change the battery (Lead Acid to Lithium), do not use the existing charger but get one the will fit your battery (a 12V charger). Make sure that whatever battery you get will have a proper battery management system that monitors charge cycles, temps etc. Something like this [https://www.amazon.com/EEMB-Rechargeable-Lithium-Battery-Replace/dp/B08FCGYSRZ?th=1|would work]