wrote:
>
> My electricity in my car was not working, so I went to a shop where
> they tested it and my alternator. They said the battery was bad, so I
> bought a new one.
>
> Now, I just bought the old one 6 months ago, so I knew it shouldn't be
> bad. The thing is, when I took it back to Advance Auto parts, they
> tested it and charged it, and it seems to be holding a charge just fine
> now. Three different machines said it was good. However, when tested
> with a Snap-On MicroVAT it showed up as bad.
>
> Now I'm confused. Obviously there was something wrong with my car a
> week ago. With the new battery it seems to be working fine. However,
> since 3 machines said the battery was good, and only the MicroVAT said
> it was bad, I don't know what to believe.
>
> Does any one have any advice?
>
There are a number of failures that batteries are prone to. Some
testors may test some but not all of these modes.

Holding or not holding a charge is only one of the failure modes
(usually an internal short). High internal resistance is another (the
limit of which is an open connection, an infinite resistance). Crack
in a cell can cause it to lose electrolyte. No electrical test finds a
cracked cell per se, but if the cell is low in electrolyte the internal
resistance will show abnormally high.