Most chargers read your alt condition, so it's relatively easy to rule it out as the problem. You can try desulficating your battery. I've heard newer cars don't like running with NO battery connected, but never heard a bad one affecting operation once running as long as there's at least something hooked up. Be glad to be told different though.
You need those codes. How many KMs on your Cady?
\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear). Finally, wait for it... LT-4 knock module!
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, yes again... LT-4 knock module!