Hey guys.
I apologize if this has been covered a dozen times.
I tried a search.
The Interstate battery in my '87 300 TD is 6 years old.
Currently 245 K miles and only 30K miles in the last 6 years.
I am thinking that it is time to replace the battery to be on the safe side with winter coming.
I asked for it to be checked at the last service but the tech seemed to be rushed and I don't know if he did, it looks like he added some water.

Also the pos pole has a little corrosion.

So Where can I buy an Interstate for the best price?
Are the different brands made by one of two companies and does it matter how long a battery has been sitting on the shelf before I buy it.
Any recommendations are welcolm.
You guys are the best.
Again sorry if these are dumb questions.

Thanks in advance.

B