I've had one of these for years, clarkemart.co.uk/product_pp.php?id=9352&catego...7

it will still start almost anything, this is the best price i can find at the moment with it looks like free delivery (if you can find it cheaper then buy it quick), and a replacement battery is available when it eventually dies @ around £75, it's a no frills jump pack though, all it has is an all important isolator switch a light and a cigarette lighter sized socket power output, can be charged with its own charging pack or faster via a normal battery charger.

Note though its heavy, its twice the width and weight of a typical jump pack because it has twice the battery inside, but the leads are long and very thick so you won't need to balance this one somwhere in or on the engine bay which can be a problem with some of the cheaper units which need shorter leads.

edit, that one linked to by Elec Doc is a bargain.

Edited by gordonbennet on 26/09/2017 at 12:33

I've seen hundreds and possibly thousands of cars jump started in my previous work, the 'yardies' who move the cars in vast compounds at docks and storage facilities often have a minubus with permanently wired heavy jump leads ready at all times clamped to a rubber insulated rail bolted to the front of the vehicles.

They don't have time for all these niceties, they very often don't even use the clamps at all but one of the lads will raise the bonnet and hold the leads against the two flat battery terminals whilst another starts the car, and leaves the flashers on if they're going to leave it running assuming its got some fuel, if for example its due for transporting, both to give the charging system a reason to work and so others know what the score is there, plus if left it could still be days later if it had enough fuel, and this has happened hence the flasher practice...the minibus engine almost never got stopped during the working day.

I too don't usually bother earthing to the engine, simply clip both terminals on the dead battery, i'm more concerned about the donor vehicle in all honesty if its a modern with the devils electronics, so for me i'd rather use a jump pack with an isolator switch than jump leads these days.

I've only ever seen one battery explode, and that was a lorry battery on an old Leyland lorry around 1977, the clot connecting up the freshly charged battery managed to short a spanner across the plates (remember when batteries had exposed metal plates between the cells?) and the spark from that contact must have ignited the hydrogen with predictable results, he got covered in acid but luckily no permanent damage, my clothes got splashed and were in effect bleached.

Edited by gordonbennet on 27/09/2017 at 09:04