Replace one bad block?

You can change the failed module but changing just the module won't get you a reliable repair. If you plan on keeping this car for 1 or 2 years, you would start to invest some time and money into this car for it to be reliable.

First thing you should do after the battery repair/replacement will be to clean out the EGR circuit and Intake manifold. These areas are the leading cause to the head gasket failing on these cars at your mileage. It's a lot of work (time wise) but without doing it, you'll end up with a real big $3000+ headache when the head gasket fails.

There are other items that would need attention after 12 years but you'll need to put some good money to keep this car running reliably. Spend money now for maintenance or spend a lot more money later.

 

You need to remove the battery, you don't really want to watch some crazy stuff and try following it. It's hard enough to do it out of the car....

 

You have to balance the pack. Prolong has a great system for this.
You might want to try that system first. It's less costly than a whole battery.
And if that block is "bad", you can bet others will soon follow.

I used that Prolong system. It took 3 days for the 4 charge and 3 discharge cycles.
If I could have monitored it better it would have been less time. But it really made a difference.
It lasted about 9 or 10 months before I noticed it slowly started the slower charge quicker discharges.

I just did a full charge, because of time, and it's been working well since.

 

I purchased it. It has the discharge and charger. And well worth the money.
It was around $700. A lot less than a new battery.

There are people out there will all kinds of time on there hand, and probably a spare battery.
They spend weeks and week charging and discharging individual batteries, then paring them,
then "balancing" them. If you have a month or so to do this, and spend the money on all the
chargers, it's probably less costly. But labor wise it's not. A lot of work taking that battery assembly
out of the car and then putting it back in. And then taking it apart, and putting back together again???
Unless you like doing it.....

Depending on where you are, there might be someone that would rent it to you. You'll have to
purchase the harness, about $150, and install it. Which is not hard to do.

I believe you can find new cells for around $50, used less, but who knows what you'll get with used?
For me, there are certain things that are just not worth the risk of buying used. Batteries of any kind
are one of them.

What you might want to try is to remove the buss bars and clean them up. And the battery contacts.
Just be careful NOT to short them! If they are corroided, it will create resistance.