There are two types of driver in this country: those who own a jump pack, and those who've stood in the rain at 7am hoping a neighbour answers the door. A modern lithium jump starter weighs less than a kilo, fits in the glovebox and will start a 3.0-litre diesel on a frozen Perthshire morning ten times on a single charge. They're one of the genuinely transformative pieces of kit of the last decade. Here's how to pick one that'll actually do the job when it matters.
Old-school jump boxes were big, heavy, lead-acid bricks that lost charge sitting in the boot and were useless after two winters. Lithium-ion packs hold charge for 6–12 months between top-ups, weigh 400–800g, and deliver peak currents that embarrass kit four times their size. Even the budget end now reliably starts up to a 2.5L diesel. If your existing pack is lead-acid, replace it.
Manufacturers love quoting eye-watering 'peak amp' figures — 2,000A, 3,000A, even 4,000A. These are the brief surge a unit can deliver for milliseconds. The number that matters is starting current (continuous over a few seconds). For petrol up to 3.0L look for 400–600A starting; for diesel up to 3.0L aim for 700–1,000A; for 4.0L+ diesels and big vans go to 1,500A+ rated units. Ignore the headline number, read the small print.
Lithium chemistry drops capacity sharply below 0°C. A pack rated for 25 starts at room temperature might give you 4–5 starts at -5°C. Reputable manufacturers (NOCO, GooLoo, Halfords Advanced) test and rate for cold; the no-brand Amazon specials usually don't. If you live in Scotland, buy from a brand that publishes cold-cranking performance.
Look for reverse-polarity protection, spark-proof clamps, over-voltage and short-circuit cut-out. A connection mistake on an unprotected pack can weld a clamp to a terminal — or worse, take out your ECU. NOCO's GB-series and the GooLoo GP-series are good benchmarks here. Anything that doesn't list these protections by name, leave on the shelf.
USB-C PD for fast-charging phones in an emergency: genuinely useful, especially if your unit is also your roadside power bank. Built-in air compressor (NOCO GBX, GooLoo GP4000): brilliant for one-bag emergency kit. Built-in torch: every pack has one, but check for a proper SOS strobe mode for breakdown visibility. Avoid units that prioritise 'features' over jump-start current rating — the basics come first.
Lithium jump packs need a top-up every 6 months even if unused. Set a calendar reminder. A flat lithium pack left flat will degrade and may refuse to charge again. Store between 10°C and 25°C if possible — not in a boot through a Scottish winter, not in a baking glovebox in summer.
Up to about 3.0L on a healthy engine, yes. For larger diesels or very cold conditions, step up to 1,500–2,000A peak.
Every 6 months minimum, even if unused. Lithium self-discharges slowly; running it fully flat shortens its life.
Most hybrids have a 12V auxiliary battery for the electronics — yes, you can jump that, and it'll usually let the high-voltage system come alive. Never connect to the high-voltage system itself.
Yes — but use the bike-specific terminals on your battery and only the smallest packs (under 800A peak) to avoid overwhelming the bike's wiring.
Short-term yes. Long-term cold or heat shortens battery life. If your car lives outside in a Scottish winter, bring the pack inside between trips.
Bob's Mechanical Repairs — independent family-run garage in Birnam, Dunkeld, Perthshire. Call 01350 727 276 or email [email protected].