Volvo: 2001 S40 Limp Mode, brake warning light, flex pipe

Question
I had been having a problem when trying to get on the car, it would start choking and sputtering.  The codes are 0420, 0600, and 0700.  I found that 2 of the codes are generally attributed to the flex pipe leaking... I have not had the money to replace.  Otherwise, it ran fine... until one cold morning it started perfectly but the battery, ABS, and Brake warning light is on and it is in limp mode.  I shut it off and left it at home, then that evening I restarted and there were no lights.  The next morning, it was dead... not even enough battery to turn on the gauges.  (The battery was not even one month old)... I took the battery back... they said it was bad and gave me a new one.  Once again, started right up but the same three warning lights are on and it is still in limp mode.  From most of the posts about limp mode and sputtering under load... it sounds like I have a fuel delivery or O2 sensor problem.  Where do I start checking? Would this have anything to due with the battery light?  I am imagining no, but I hate to pull the alternator out again as it was replaced last year.  Thank you for any help you can give.

Answer
Jessica,
First read the fault codes and follow them replace and repair as needed. Clear the codes see how the car will run. If you start fixing the known faults you can then move on to the rest. Running it with faults might not be the best thing to do depending on the faults.
The battery may have been a bad one. Have the charging systm tested to see if it will pass a charge test.