How we check

Our method is a claim ledger: for every product, what the box says, what the maker's own fine print says, what a standard or public record says, and whether it fits your car. Here's every step, so you can check our work.

  1. Save the exact claims. We read the maker's product and spec pages and the Amazon listing, and save the exact wording with the date and link. Every rating on our pages points to that source.
  2. Rank the sources. The maker's own site comes first. An Amazon listing is written by the seller, so a claim found only there is marked "Amazon only." A seller's blog is marked as a seller's blog. For how-to steps, we use the maker's instructions and the vehicle owner's manual.
  3. Flag what doesn't add up. When the listing and the maker disagree, or a listing contradicts itself, we say so on the page and show both numbers.
  4. Match to your car. Our fit tools use your engine size and fuel, or your VIN decoded by NHTSA's free vPIC database. The VIN goes straight from your browser to NHTSA; we never see or store it.
  5. Pick by a written rule. Each page states its rule before the pick. For jump starters: the maker must state the engine rating and the battery size, on its site or in its manual, and the rating must cover your engine. We suggest about 2 L more for freezing mornings; that 2 L is our margin, not a maker's. No pack we checked has 2 L to spare over a 6.6 or 6.7 L truck diesel, so for those we pick the cheapest pack that covers the engine and name the one with the most room.
  6. Keep prices honest. Prices come from Amazon's product API and show the date we read them. Picks that go out of stock are swapped, not left as dead links. Tables that list every product we read can include one Amazon no longer prices, marked as such.

Where the numbers come from

Ratings and specs are the makers' own, read from their sites, manuals and Amazon listings. What owners report comes from reviews we read, each one cited. When we cite an independent test, we name it and link to it.

Our data

Pages with tables offer the data as a CSV download, free to reuse with credit.

Last updated October 24, 2026.