Batteries in Paralell

[bryanmole]

I am new to the motorhome scene and have just purchased a C15 K reg in good condition, my leisure battery is an 85amph, I have another 85amph and wouild like to put these in paralell to give me 185amph, how do I go about this, and is it safe.
Many thanks
Bryan

[ant]

Hi Bryan.
That may seem like an easy solution to increasing your battery power but its not quite as simple in practice. Yes by connecting the batteries together in paralell you'll give yourself more battery life, however if you have a battery that is vastly bigger (in terms of what charge it will take) than the vehicles starting battery you will upset the charging of the alternator priority. The alternator would normally charge the vehicle battery first( just because it's nearer with heavier leads), then once the alternator light goes out on the dash a relay joins the batteries together and charges together. If you connect two batteries together and one is flat the charged battery will discharge into the flat one, then the alternator will charge the pair. If you have one battery much larger than the other you effectively flatten the vehicle battery far more than is desirable before it starts to recharge properly.
I would be tempted to fit a single 110amp/hr sealed battery, takes up less space and is about as big as I,d go with a 70amp/hr starting battery.
Ant

[bryanmole]

Thanks for the advice, having read your reply I have decided to stay with the one bettery that is now on board, when that needs to be changed I will get a larger single leisure battery, thanks for the advice.
Bryan