A reader wanted to know how to charge his Acer laptop from a narrowboat. Using his knowledge of charging from a car's cigarette lighter port, our Helproom Expert explained.

QUESTION I'd like to charge up an Acer Aspire 5741 laptop using a 12V (300 amp) battery with no inverter on a small narrowboat. The battery is used to start up the engine and provide power to the internal lighting and water pumps. Is this possible and, if so, how? I don't have a 12V car-style cigarette-lighter socket in the boat at present, but I'm sure one could be fitted. Nick Steinitz

HELPROOM ANSWER No laptop will require anything like 300 amps, Nick. A more realistic maximum is closer to 5 or 6 amps. The problem you're most likely to run into is that laptops typically use power supplies running at more than 12V. The Acer Aspire 5741, for example, uses a 19V PSU rated at 4.74 amps.

If you're willing to fit a cigarette-lighter socket, then a car adaptor is likely to suit your needs. You'll need one with an adjustable output voltage that supports 19V. Maplin sells a 120W adaptor with a selection of interchangeable tips for the laptop end of the cable. We haven't been able to test this, so you would need to ensure that one of the tips fits – perhaps by visiting your local store.

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