Battery Short (Internal)

I have had several batteries (Napa) that have developed an Internal Short... last one max charge at 7.5 volts... and extremely hot.
Maybe you can offer a suggestion.
I may have a severe Car problem ...
Car is 1985 Cadillac Eldorado

I am now on my 4th battery in 1 year...counting the one in the car before it was replaced last December.

It seems that, at least the last two (2) new ones developed a "short circuit" within the battery.

they were brand new, from NAPA, shipped within a month or so of installation.

Napa has honored the warranty... however it is a hassle to have this problem.

The last battery was installed about 4 weeks before it was DEAD ,,, which occurred while I was gone out of the country for 3 1/2 weeks.

So, one would think it is simply power drain or the Alternator.

But,
The Alternator "appears" to be putting out 14.5 volts steadily while car is running.
I spent most of the weekend disconnecting various components and removing all fusses I could find... and tested for short circuits...
found none.

and tested alternator , basic Diode test.

Any ideas..????.

3rd brand new battery went in yesterday...

NAPA store records show that they have sold approx. 100 of these batteries in last year, and about 5 were returned... 2 were mine a couple were from airport equipment that is used constantly.

Ideas?

The alternator should drop back to less than 14 volts when the battery is charged.

If not it just cooks the plates and short circuites as it melts the dividers between cells.

That is why they make trickle chargers to keep from burning up batteries with no load on them.

Later,

Sounds like you have a short. Maybe time to visit an electrical shop. I'd check the wires going from the battery to the starter first.