Above: the Benex Dynamo Torch, which forms the basis of our emergency power plant.

Back in the 20^th century, it used to be said that you really knew you were a parent when battery costs for your kid’s toys exceeded monthly power bills.

Fortunately, recent spectacular improvements in rechargeable technology now offer cost-effective secondary batteries and chargers – and at keen prices.

NiMH "AA" cell energy capacities have near tripled from 750mAh to well over 2000mAh since the year 2000.

It’s assumed you’ll have a nearby mains outlet for recharging – but many occasions arise (commuting in a peak-hour train maybe) when you’re away from such facilities but with hi tech toys crying for a top up.

Such an occasion arose recently, when bad weather meant a mate on a weekend walkabout, hunting in a nearby but isolated NZ mountain region became hut-bound for nearly a week – trapped by a flooded river.

Although warm and dry indoors, the batteries in his mobile phone, radio and torch all progressively ran flat. Even his digital camera, intended for the 12-pointer deer he’d hoped to shoot, gave up!

Perhaps a solar panel would have helped, although the scudding winter rain clouds, which caused the flood in the first place, rather hinted otherwise.

Above, winding the handle produces the power to charge the batteries.

In despair at his "Joule less" plight, he even took to the old trick of warming batteries in the oven and chewing their outer casings to persuade a few more electrons to flow...

At least he had an ultra bright white LED torch! Let’s face it – these efficient lighting devices have been one of the most benevolent developments in decades. But even they typically only offer 80 hours on "lite" mode – perhaps a week of evening use if half charged.