I kept all of the receipts and paperwork for my parts purchased.

For the batteries I have it in a folder. I figure when it is time to replace it I'll pull out the paperwork and take advantage of the warranty.

I don't remember the type of battery right now and I keep all of the receipts in the car.

If the battery sucks then show them the receipts and return/replace it when necessary. No need to worry about whether or not it's going to last long.

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-Typos courtesy of my mobile phone.