Catalytic Converter bad causing drive bat to fail

If the cat converter was clogged badly enough to keep the engine from starting, or running decently, I could see it being an issue.
I drove my white 2005 for about a year with an amatuer rebuilt battery with the 420 code and never had a problem, until it was run off the road by an SUV, that car was still averaging 48-51 mpg.

If you had 'engine fail to start'/ engine weak/etc codes along with the 0420 code, then maybe I could believe the cat was clogged badly.

Did they tell you what the actual fault code was?

 

Advance Auto Parts - Down for Maintenance

I am sure there are gaskets as well. (this is 48 state legal, not CA or NY)

 

rebuilt battery companies will use any excuse not to fulfill warranty claims. you're lucky they gave you another.
does your car pass emissions?

 

NO.
But if the CAT is going bad you need to get that fixed TOO.
It may be putting some additional "strain" on the engine......but not the battery.

 

I have heard of that too, but don't know exactly the dynamics. I don't think the catalytic converter has any impact on the battery

 

Keep in mind that a severely damaged/clogged cat can reduce engine power significantly, which in turn, can cause the HV battery to be loaded/cycled quite a bit harder than usual. Most "refurbished" batteries are already a bit sketchy, so there's no telling how well they'll handle the additional cycling/loading.

Now, that being said, my white 2005 (may it rest in pieces) had a P0420 the entire time I had it (about a year). That puppy had 280k + miles and was still banging out great mpg every tank. That one had an original 2005 HV battery (removed from my blue 2005) which had one failed module replaced with a 2006 module by the previous owner and his son... It never had a problem.