Instant cure for a flat battery - anybody used a JUMPSTAR?

[alanXK8]

Dear all, as we all know a low battery voltage can cause all kinds of issues on the XK, and also the battery itself is a bit of a devil to get at. In this weeks' paper I saw an advert for a JUMPSTAR, which is a small device (fits in the palm of your hand) that plugs into the cigar lighter socket and, they say, will recharge your battery sufficiently, in a few minutes to start the car. Then you leave it plugged in for a while and it recharges itself for next time. So to my QUESTION: Has anybody used one? Do they work ok? Can they damage the Jags systems? At the moment they have a two for one offer which at £30 is extraordinarily cheap - if it works!!

[Orkney]

Hi,
I've been looking at those for my XJ8 too and am a little confused at the technology behind them. The wiring and fuse protection to a cigarette lighter is certainly not capable of providing sufficient current for a starter circuit! So, unless you leave it for a considerable time at a low current, I fail to see how it can quickly start a car - probably OK if the battery is only just 'off the mark' That said, I have an MPI Mini Estate which I built myself and installed a cigarette lighter socket for accessories and I have made up a lead which I plug into that socket to keep the battery occasionally topped up from a normal charger as that battery is also difficult to access.
Additionally, I believe the XK8 and my XJ8 are similar in many respects and on mine there are 2 access points (rubber covered) under the bonnet to connect a charger to - something I did for a friend who had left his XJ8 in a totally inaccessible place in his garage when the battery went flat. No ill effects after an overnight charge - so maybe these units are worth a punt.

Ian

[mike020150]

Hi Alan,
As Ian says, the cigar lighter is protected by a 15amp fuse so plugging in a charging source for half an hour could only add a max of 7.5 amp hours which isn't much charge for a car with a battery rated at more than 100+ amp hours. Stick with the battery conditioner. It's a safer, more reliable option. Mike.

[alanXK8]

Hi to Ian and Mike and thanks for the responses. I have phoned up the supplier and spoken to their 'technical advisor'. Two things emerged, firstly he did not think that it had enough power to restart a 4.0 litre engine, so not confident it would suit big monsters like ours. Having said that, I didn't mention the potential issue of overloading the cigar lighter circuit and he replied that they had sold loads of these and not had any of them returned for that reason. also, they were ready for use immediately they were plugged in, so could still be a good thing for smaller engines? Any body else actually tried one? Best regards, Alan

[Orkney]

I wouldn't really want to be too negative about the technical advisor (I noticed you put that in quotes!) but to say they are ready for use immediately must be suspect - Mike's figures are obviously spot on, so with a flat battery, the only place the current needed can be drawn from, is via the cigarette lighter circuit. I would also be suspicious about his blanket statement about 4 litre engines - these are V8's and have twice the number of firing events as a 4 cylinder unit. I would imagine it would struggle to start my Berlingo Van with only 2 litres, but around 22 to 1 compression ratio (it's a diesel!) I'll bet Mike's V12 Daimler is easier to fling over than the average 4.
This would not stop me from asking what the max output current at a bit less than 12volts (low battery) would be, before I shelled out any brass.
As Mike said just use a normal charger - especially if the XK has underbonnet access like the XJ.
Ian