Let me try to explain how the warranty works in detail.
First, the CPM is the RETAIL or MSRP divided by the months of warranty. The Retail price used is the price of the battery when the battery goes bad, not the price when you bought it. We never sold a battery for the retail price but for the wholesale price. If the battery has a 60 month warranty and a 2 year replacement warranty then the battery would be replaced free of charge for the first 2 years. If the 2 years was up then you would have to pay the CPM from the day you bought it, figured on Retail price at the time of the warranty.
In other words, If you buy a battery now and paid $100 for it but the MSRP may be $130. For the first 2 years (or what ever it is) you will get a free battery. If however the battery last 30 months and the MSRP of the same battery is now $140 you will have to pay $140/60X30. That comes out to $70 for a new battery. At 40 months it will cost you $98. Try to explain that to a customer. Now, if the price of the battery didn't go up and you paid MSRP for the battery then you would come out even at 60 month as promised.
Now with Interastate batterys, there was never a question about a warranty. If you said you wanted a battery warrantied during the replacement time because you like the color of the newer batterys better, they gave you another battery with no questions ask. You can't beat a deal like that.
For years I only drove my 500SEL on weekends and sometimes not even then. Batterys would only last for 2 years max, so every 2 years I would get a new battery free. I told them that the car would set for extended periods and they just said, "No problem, here's a new one".

Paul

P.S. We sold Interstate batterys for about 27 years and never had a problem with the company. We did see some problems with the batterys but they always took care of them. They replaced some free that were out of the replacement warranty. The route man could make that decision with out calling in.

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84 500 SEL (307,xxx miles)