I'm trying to make charging a 12vdc kids ride on toy a little easier and also possibly upgrade from 12 to 24vdc at a later date. The issue is that the LiFePO4 battery and NOCO charger are rated at 12vdc and if I upgrade to 24vdc I will have to be able to switch from serial to parallel wiring. I figured I could do this automatically with some sort of relay, but I'm mot experienced with circuit design. Below is a diagram of what I am thinking. Basically the relay for the 2nd battery would be managed by a switch and a relay independent of each other. If the switch is off and the charger is not plugged in, then the system is set to 24vdc. If the the charger is plugged in, then first relay (K3) is activated and disconnects the wiring harness to the toy (M2) and activates the 2nd relay (K4) such that the wiring is parallel. If the charger is not plugged in and the switch is toggled on, then the 2nd relay should activate resulting in parallel wiring. I added some diodes to try to limit surges for the relays and try to protect the battery charger in the event of a malfunction, but I'm not really sure what I need until I can get the items on the bench to test. My hope is that someone can look at the basic design and (A) confirm the design is accurate and safe, and (B) advise what changes or areas I may need to changes I should study as I'm a complete noob and am willing to do my homework and learn. Thanks in advance for the assistance!!