From what you said, just buy a 48V 10Ah lithium iron phosphate battery. The price is around 1,800 yuan and comes with a charger. The volume and weight are much lower than lead-acid batteries. You can go online and find the seller yourself. However, I purchased a 4810 lithium iron phosphate battery module and did a charging and discharging experiment and found that when the discharge current is greater than 10A, the service life decreases rapidly .
The security issue is not serious. The lithium battery is sold as a single module and has a built-in protection system. It will not explode in the event of a short circuit. but do not leave it in the battery during exposure to sunlight.
Replace or not, it depends on your personal wishes
If the output voltage of your headlight is 48V, you can connect 15 LEDs in series without limitation of coresistance current, then directly plug in the power supply. If you think that's not enough, connect another group of 15 LED lights in series and parallel. There is no need to use resistors to limit the current. The power is not large, so the heat dissipation problem is not taken into account.