Just a thought before everyone bombs the poor guy to oblivion,

What about if masgra is intending a second battery to double the length of time he can use appliances whilst parked up, lights etc whilst camping?

If the bike were stock there would be plenty enough surplus to charge both batteries whilst riding and with a split charge system fitted correctly you could then use the auxillary battery when stopped to power whatever you like without draining the main one.

Is this the intention?

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I'm always in the sh1t, only the depth varies