Saw this when disconnecting my battery to remove the alternator as part of the timing chain gasket process. I drive the car a couple times a month normally with exception of it sitting the past 4 months waiting on parts to fix my leak. I keep it on a maintainer when not in use.

What could cause this to be so bad and anything I can do to prevent it? Wire is basically welded on so going to have to replace it and battery so would like to take steps to prevent this. I've had minor corrosion on other cars but never this bad nor on a side post battery.

Picture bellow is after hitting it with a wire brush and even chipping some off with the end of a screw driver. Fortunately I found it before it stranded me.

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