Tool
Car Battery Warranty Calculator
Enter what you paid, the warranty terms and how long you've had the battery. We'll show a free replacement or a prorated credit.
Last updated October 2026. By the editorial team.
Free replacement or credit?
How to use this tool
1. Enter the price paid
From your receipt.
2. Enter the warranty terms
Free replacement months and total months.
3. Enter months used
How long you have had the battery.
4. See the outcome
Free replacement or a prorated credit.
The Maths
Within the free period you get a replacement. After that: credit = price × remaining months ÷ total months. At $150, 24 months used, of 36 total: 150 × 12 ÷ 36 = $50. Some brands calculate the prorated period from the end of the free period instead. Check your paperwork. Terms vary by retailer.
Frequently asked questions
What is a prorated battery warranty?
After a free-replacement period, you get a credit toward a new battery that shrinks as the battery ages, instead of a free one.
Is the formula the same everywhere?
No. Terms vary by retailer and brand, so use this as an estimate and read your warranty. Costco, for example, is described as a 36-month prorated warranty (third-party; verify on costco.com).
What do I need to claim?
Usually the receipt and the battery. Ask the seller; terms differ.
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