Some chargers have a 100 amp "start" feature where you can hammer them for a while to get them charging. As Steve says, they aren't bad batteries. Most batteries last a very long time-- they are usually killed by their operators. I personally like the Sonnenscheins and recommend them.
Anyway back to the coil, you probably searched here for "Brazilian" coil (careful what that brings up in the Off-Topic Forum
) - you may want to check the primary and secondary resistance of the coil to verify it's within the specs for the old Bosch "black" coil bearing the same part number.
Do you have any photos of your wiring? That is always a help for remote diagnosis.
Good luck, the answer is not far away.