March 29, 2006 12:21
Copprhead Wrote:If you get only 12.8V with fully charged batteries, there is something wrong.
applies also to your extension cord, it might be too thin. We have the same problem with our fridge. With extension cord the fridge only runs with really full batteries, then the voltage gets too low and the fridge stops voluntarily to protect the battery from deep discharge.
Actually, if the motor is not running (no alternator) then a reading of 12.8volt IS a charged battery. The gauge of you extension cord will affect the voltage drop to your Mac. The car adaptor is designed for a car which usually has the engine running (hence an alternator putting out charging voltage >13 volts). There are numerous adaptors out there (DC-DC convertors) which are more appropriate for boat use, check out the iGo products.