Help Diagnose: Motor Cuts off when light is on below 63v

Hello Everyone,

I purchased a used Ebike, its 60v with 16s18p lithium, during winter time changed the lights to LED.
tried it for couple rides, it rides nicely, and the battery is ok, for reference 16s battery
67.3v is 100%
60v is 50%?
55v is safe low voltage

if the bike has no lights on, the bike runs fine, the throttle is responding fine,
but if the lights are on, the throttle responds as long as the voltage is over 63,
if voltage is below 63, I have to turn off the light for the throttle to work, I can even turn on the lights after (while my hand is on the throttle) but if I let go I cant throttle again until I turn off the lights. so only the start of throttle doesnt work if the lights are on..

so in a night ride, I would have lights on at the start, no problems
when the battery voltage gets lower, while climbing hills (as voltage sags more) it starts happening,
until voltage is below 63 then I would have to turn off the lights for the throttle to work.

I first thought it is the battery not providing sufficient current but its a huge battery, and when I turn off the lights, the battery still runs at least another 20km, going uphills like a champ no problem

I am going to try to swap the regular lights back and maybe change the controller (I have a spare) to try, see if it helps,
also I noticed that the DC/DC converter is from 64v-48v, could it be the culprit? since probably the lights use it to convert to 12v?

I dont feel like riding at night anymore for safety, what do you guys think the problem could be?
your input is appreciated

Your battery sags under the load of the lights I think. Its getting pretty weak then I'd think.

It it a factory bike, or a bike someone converted? Were the old lights being powered by the buck converter too?

Sorry for the late reply, i was busy, I really appreciate your replys

I doubt it is the battery because it gigantic, and its only LED lights
but the fact that it sags that much on regular load kind of worries me. Anyway I just got an big order of 18650s so I am planning to make a new battery pack and see if the issue is resolved when a new battery is hooked..

Yes it looks like it came from the factory with that converter, but I could be wrong, maybe it is not wired to the lights, maybe it was made for a mp3 player or something. I have to disassemble the bike to its barebones cuz the wires are deep inside. I will do it this week. I will figure it out.