"Jens K" wrote in message
om...
As a very basic answer, a 100 amp/hour battery should provide 100 amps
for
an hour or 1 amp for 100 hours, in reality of course it would probably
melt if required to do the former. Then you need to factor in age, type
of
use, deep charge trickle or whatever. At best it is a guide only as to
the
possible maximum the battery can provide.

As I normally daysail I do not need a battery in my boat. But when I
occasionally cruise for a few days, I would like one, but only for the
lights. I do not have other power consuming devices in my boat.

So now the question is this: could I simply move my car's battery to
the boat? Let's say for a four days cruise during summer time. Will it
still start the car afterwards? I guess there will be the pleasant
side-effect that the car will be less likely to be stolen.

Please do a power audit (www.reading-college.ac.uk/marine) under course
notes. This will tell you exactly how much electricity you need to store.

Then decide if teh battery will still have enough capacity left to start the
car in adverse conditions (my guess is no).

If you do decide to go ahead with your proposed plan, please be aware that a
car battery is constructed differently to those designed for the use you
have in mind and you will shorten its life. If it is going to be by a
measurable amount, I have no idea, butw ould not take the risk.

I suspect a small leasure battery from a caravan shop and a split charge
relay for the car (from the same source) would be your best bet. You could
even just run a wire from the ignition switch to a croc clip in the boot to
recharge the leasure battery whilst driving.

Tony Brooks