2004 Chrysler Sebring convertible starting issues

So I bought a 2004 Chrysler Sebring
convertible about two weeks ago.
The car ran fine when I test drove it
and a few days after. Then a couple
days later the check engine light
came on and then a few hours later it
went off. We went to autozone and
had the code pulled, and the guy
told us it was a dealer code so I
googled it, P1391... Which
apparently has to do with timing and
or camshaft sensor or camshaft
issues. The guy told me it made a
quiet slight ticking sound when
running and said it was probably our
camshaft. So far it has not gotten
louder. This past weekend we started
having issues with it starting which
seemed like a dead battery so we
were able to jump it. After sitting for
long periods of time like over night,
we would have to jump the car to get
it started or pump the gas pedal
while cranking it for it to start. This
past Monday we had the charging
system tested and the mechanic said
it came back inconclusive and he left
it at that. On Tuesday night we went
to autozone to test it and he said it
had 11 volts while off, so it may be a
bad battery and then he used his
battery jump to start it again. The
next day it would start at al. Not even
after trying to charge and jump it for
15 minutes. Every time we tried it
made this knocking sound when
trying to crank it. We still have lights
and radio each time. Last night we
charged it with my uncles car for
about a half hour and they were able
to get it to start again. And then
today they were able to start it three
times and still drive it. It still makes
the slight knocking sound when
trying to start it by pumping the gas
pedal, and then it revs and is started.
Today we checked out the fuses on
top and it looked like none of them
were blown or broken. We took the
tire off to check out the battery
cables connected to the battery and
none of them were loose or coroded
and neither were the ones on top
where the posts are and the cables
connect on top when you pop the
hood. I am at a complete list on what
to do next or what to check out.
Does anyone have suggestions or
insight on what could be going on?
The dealer sold me this car as is with
no warranty so I can't even call
lemon law on it-.-