Travel gadget: Porta-Jump

There's nothing more annoying than coming back to your car and finding the battery is flat. It's happened to me twice. Once as a result of leaving the lights on, the other time due to a curious grandson turning the wrong switch. What do you do? Wait for someone to come along with jumper leads? Ring the AA (if there is an AA)? Start walking?

At first glance, the Porta-Jump - a small, portable battery, about the size of three packs of cigarettes, packaged with circuitry designed to recharge your battery in an emergency - seems the perfect solution. In a nutshell, plug it into the car's cigarette lighter, wait five to 10 minutes , then start the car. Plug it in for 30-40 minutes and it's recharged for next time.

But when the Herald tried it on a 2009 Subaru with a factory-fitted immobiliser, it wouldn't work. The instructions do warn this can happen with some modern cars equipped with sophisticated anti-theft systems. Unfortunately, discussion with local auto-electricians suggests that these days a high proportion of modern cars have such devices.

If you're going to be using an older car, then the Porta-Jump is an excellent back-up. But be aware if your car is a modern model, you're probably going to be on your own if the battery goes flat.

The Porta-Jump is on sale at hardware and automotive shops from around $50-$60.