battery

I have been using one of my deep cycle batteries to start my coach since my starting battery has died.The funny thing is it reads fine with the multimeter.I have one of those 40amp three stage chargers and when i check the battery voltage it says 14.4amps.It trickles from 7amps down to 1.8 and i try to start it nothing but an urr.The charger immediately goes back up to 7amps.I have tryed a quick start and nothing.I tryed jumping it with jumper cables from one of the house batteries and it started.That is how i came down to the temporary solution of disconnecting one of a bank of two house batteries and connecting the starting cables to the house battery.My question is how long can i get by with this before trouble and is it normal to have reading like these with a dead battery?The voltage with the mutimeter read 12.30 with out engine running and 13.8 when engine running???