after getting the battery pack open, i noticed there were two fuses. one of them was burnt. i swapped it with a new one and threw it on the charger, and it started charging! as for the black bike, the batteries (it came with two) seem fine. the rear derailleur needs adjustment as the chain keeps slipping off when shifting. this will be done over the weekend as the weather warms.
my partner and i expected the worst, having to spend $550 for a new battery for each. instead, it seems we got the luckiest deal on two bikes today. $106.95, if we’re counting the 5 pack of fuses.
-- cont. 16 February 2025:
today, we got the bikes cleaned up and took them out on the property. we made lots of adjustments to them over the course of the day, starting with a basic fitting. partner loves their bike, they put a basket on the back and carried firewood back to the house in it tonight. their bike is in great shape with less than 200 miles on it. mine was someone's daily with nearly 4800 miles on it; guess that explains the slop in the derailleur and all the marks on the frame. current plan is to take the black bike into a local diy shop and get it fixed. i've done all i can at home with limited tools.