Common questions
22 questions, answered directly, each linking to the page that goes deeper. Where a figure comes from a manufacturer or a regulator, the page it came from is linked there.
Jump starters
- What size jump starter do I need?
- Match your engine's displacement and fuel type to the manufacturer's published engine rating rather than comparing peak amps. A 1,000-peak-amp pack is typically rated to 6.0 liters of gas engine, which covers most cars and crossovers. A diesel needs roughly double, because diesel ratings run about half the gas figure at the same pack capacity. More
- Why do diesels need a bigger jump starter than gas engines?
- A diesel ignites fuel by compression rather than a spark, so its compression ratio is far higher and the starter turns the engine against more resistance. Glow plugs or a grid heater also draw significant current before the starter engages. The same pack is therefore rated to roughly half the displacement for diesel. More
- Will a jump starter work on a completely dead battery?
- Usually, because the pack supplies the starter's current directly rather than relying on the battery. It will not work if the battery has an internal open circuit, a shorted cell or frozen electrolyte, and some packs will not engage below a minimum detected voltage without using a manual override. More
- Are peak amps the number I should compare?
- Not across brands. Peak amps has no standardized industry test behind it the way a car battery's cold cranking amps does, so a 4,000-amp claim from one brand and a 2,000-amp claim from another may be measuring differently. Compare the published engine rating in liters, which the manufacturer warrants. More
- How often should I charge a jump starter?
- Every three months whether you have used it or not, and always immediately after use. Lithium self-discharges slowly but it does self-discharge, and a pack at partial charge has lost some of the margin you bought it for. More
Travel and storage
- Can I take a jump starter on a plane?
- Yes, in carry-on baggage only, if it is rated 100 watt-hours or less — which covers every mainstream automotive jump pack. Between 101 and 160 Wh you need the airline's approval and may carry at most two. Spare lithium batteries are never permitted in checked baggage, and the terminals must be protected from short circuit. More
- Is any jump starter actually "TSA approved"?
- No — there is no TSA approval scheme for jump starters. What exists is the watt-hour threshold, and a pack either sits under it or does not. The TSA also notes that the final decision at a checkpoint rests with the officer. More
- Can I leave a lithium jump starter in a hot car?
- You can, and it permanently costs capacity. Sustained heat is the main driver of ageing in lithium cells, and a parked car's interior runs well above ambient. Keep the pack in the cabin out of direct sun rather than the trunk, and check its charge before you rely on it. More
- How do I convert mAh to watt-hours?
- Divide the mAh figure by 1,000 to get amp-hours, then multiply by the nominal voltage. A 20,000 mAh pack built on 3.7 V cells is 74 watt-hours. Without the voltage the conversion is impossible, which is why mAh alone is not a capacity and cannot answer the airline question. More
Tire inflators
- What PSI should my tires be?
- Use the figure on the Tire and Loading Information label in the driver's door jamb, not the number molded into the tire sidewall. The sidewall figure is the tire's maximum cold pressure and is often 15-20 PSI higher. Check when the tires are cold, before driving. More
- Why won't my inflator fill a truck tire?
- Thermal protection. Large tires need a large volume of air, the motor heats as it works, and the unit shuts down to protect itself. It is not broken — it is undersized for the volume. A battery-clamp compressor with a real duty cycle is the right class of tool. More
- Are built-in inflator gauges accurate?
- Accurate enough for routine top-ups, but they vary unit to unit even within one model. Check yours once against a separate stick or dial gauge, note the offset, and work around it. We publish no per-model deviation figures because we do not measure them. More
- Should I use sealant or just add air?
- Add air if the tire holds pressure — that covers slow leaks and cold-weather drops. Use sealant only when the tire will not hold air and you have no usable spare, because sealant can foul the TPMS sensor and turn a repairable puncture into a tire replacement. More
Battery chargers
- What amp charger do I need for my car?
- Around 10% of the battery's amp-hour rating, which for a typical 45-70 Ah car battery means a 5-amp charger — it recharges overnight and maintains afterwards. Use 10 amps for trucks or deep-cycle banks, and 1-2 amps for motorcycles and mowers. More
- What is the difference between a charger and a maintainer?
- A charger supplies enough current to refill a discharged battery, typically 5 to 10 amps. A maintainer supplies 1-2 amps indefinitely to hold a full battery against parasitic drain. Modern units do both, and the amp rating tells you which job the unit is really sized for. More
- Can you overcharge a car battery?
- With an old unregulated charger, yes — it keeps pushing current regardless of state of charge, boiling water out of the electrolyte. With a modern multi-stage charger, no, because it drops to a float voltage once the battery is full. More
- Can I leave a maintainer connected all winter?
- Yes, with a modern multi-stage unit — that is the intended use. Check the connection and, on a serviceable flooded battery, the electrolyte level occasionally. Also confirm the unit is still powered; a tripped outlet is the failure people discover in spring. More
- Do AGM batteries need a special charger?
- They need one that supports AGM, via a dedicated mode or automatic chemistry detection. AGM wants a different absorption voltage from flooded lead-acid, and a flooded profile leaves it chronically short of full. If your car has start-stop it almost certainly has an AGM or EFB battery. More
About this site
- Why don't you publish prices?
- Because we have no live price feed, and a stale price is worse than no price — it either talks you out of a good buy or sets you up for a surprise. Every buy button reads "Check price on Amazon" and sends you to where the current price actually is. More
- Do you test the products you recommend?
- We do not run instrumented lab tests, and we say so on every page. Picks are reasoned from manufacturer specifications, retailer listings and published owner feedback, with every figure linked to its source. We publish no measured fill times, cranking currents or gauge deviations. More
- How does Clamp & Crank make money?
- Affiliate commission. We participate in the Amazon Services LLC Associates Program and earn from qualifying purchases at no extra cost to you. There are no sponsored posts, no paid guest posts and no link sales, and commission does not influence verdicts or rankings. More
- Why is there no testimonials section?
- Because there are no reviews of this site to publish, and inventing them would be deceptive. A clean page with no testimonials is the honest version. More
Question not here? Ask it — the contact form goes to one inbox, and several pages on this site exist because somebody asked something we could not find a good answer to.