You would seem to have a parasitic draw, big enough to draw the battery down in short order. If some or all of the ambulance stuff is still in place I'd suspect one of those electrical components to be the culprit. Do a test to see what is causing that draw---anything one amp or higher will drain a battery over 24 hours without any problem.

Even though your voltage meter shoots up under acceleration that doesn't necessarily mean the internal regulator is working properly. Voltage is but one indication of what the alternator output is---you need amperage to recharge the batteries.

Hope this helps!