A couple of notes that nobody has mentioned here. Sears contracts with both Exide and Johnson controls for their Diehard brand... in some parts of the country you get one or the other.
Several years ago they were involved in a lengthy and well publicized court battle with Exide over their high failure rate. If you look it up you will even find mail fraud charges, as Exide faked some tests and mailed them to Sears!
A Walmart Everlast battery I bought about 6 years ago ( the smallest one they sell, 29.95) says Johnson controls on it and is still working well.
A walmart Everlast I bought 2 years ago says Exide on it... and is corroding badly. Exide was still using lead plates alloyed with antimony last I knew, and they still outgas quite a bit.
The Johnson Controls batteries are lead-calcium and do not outgas hardly at all, and generally do not corrode the terminals.
Those of you with an unregulated battery charger can easily tell which type you have:
A lead- antimony battery will never go much over 14.4 volts and will accept about 2 amps at that voltage even after they are fully charged. That, of course results in electrolysis, with attendant loss of water and outgasing.
The lead-calcium batteries... when fully charged... pretty much just shut the door on incoming current, the voltage may rise well above 15 volts with less than one amp going in.
They never need water added, as the pretty much totally avoid the electrolysis by no longer accepting incoming current.
Running this test, you will find the two types are markedly different!
Lead Calcium batteries also have a very low rate of self-discharge... just losing their charge sitting around. They easily hold a charge for 6 months or more when stored - with no load.
Lead Antimony batteries autodischarge, they can loose 1 percent a day and be considered normal.
Nobody but Exide makes lead-antimony batteries anymore to my knowledge.