I can't see how the batteries will affect the magneto which is a device that
generates it's own power (that is why they are used ;-).
However if it is an electronic ignition system I still can see no reason why
the two batteries in parallel will worry that, in fact it should give you
the extra capacity you want.
Are you perhaps refering to the charging circuit for the batteries ?? if so,
generally in modern equipment the alternator is self limiting if asked to
supply more current than it is capable of and I would think that your idea
should work for you without damaging the alternator. If you manage to
discharge both batteries it should be simple to disconnect one battery to
allow a faster recharge.

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Regards ............... Rheilly Phoull

"Belgian" wrote in message
.. .
Hi , i was wondering if there is any danger to fry the magneto of an
outboard 40hp Suzuki engine if install 2 12 volts battery in parallel .
I do use lots of 12 volt equipments on the pontoon, so i figured that 2
batteries would last longer .And last year a battery died on me in the
midle
of the lake. I just bought 2 brand new marine ones .
would that be too much strain on the magneto ?
thanks for your help !