You have the original pack too? Use it while you convert the second pack back to to a proper charger connector.
A male RCA connector with 48V hanging on the exposed pin, and I assume it's in parallel with the battery in the bike... That's a easy short circuit for the bike waiting to happen. No good on the charger either, now that I think about it. Really bad thinking.
XT60's and XT90's are bad enough with the two exposed pins inside the housing. Lunacycle sent me a battery with the charger port using a male XT60. The little hex head screws on any bike fit in there perfectly. ZAAP!