Thread: Duel battery set up

Originally Posted by tonyf

it is not really ideal to have an AGM in parallel with a wet cell battery and I over-ride the isolator with a battery switch to sue two batteries for winching.

Hi Tony and this is just a myth and you can ignore it.

You can safely parallel any type of lead acid battery with any other type and will not have any different problems that you would have if you had two identical batteries wired in parallel.

Furthermore, there is no reason to separate them by over-riding the isolator and only linking them for winching.

Different types of lead acid batteries will cause no adverse effects on one another if they are left parallel connected for months or even years at a time.

In many cases, it can actually be very beneficial for both batteries if they are left connected in parallel.

OK thanks for that. I trust your judgement and use one of your isolators. I usually want the batteries separated so that the frig can run one down without loss of start power. I did think that the different battery types can be charged at different rates so that uniformity allows both to be charged together with my 240v charger but perhaps I am mistaken there also.

Hi again Tony, because you will be recharging your batteries by your alternator, most of the time, it is much better to let my isolator SHARE the load over both the auxiliary and cranking battery, both while charging and while in use.

This has a multitude of advantages over using one battery at a time.

My isolator will make sure you do not accidentally discharge your cranking battery to low, so there is no need for you to worry about that side of it.

By letting the load be SHARED over two batteries, you not only place less stress on the two batteries ( this helps to extend the battery's life span ) but because of the way lead acid batteries work, the lower the current draw applied to them, the more energy they will actually make available ( Peukert's Exponent ).

Another important advantage is that even if you only use the same amount of battery energy with a two battery setup as you would with a single battery setup, neither of your two batteries will be as discharged anywhere as low as a single battery would have to be. So you will fully charge the two batteries in a much shorter drive time, and this in itself has a lot of advantages for helping to extend both battery's life span.

Tony you did raise one point that should be covered.

When charging a number of different battery types when they are wired in parallel, there are no special needs required when charging from an alternator. Just connect all the batteries together and let an alternator do what it is designed to do.

But when charging from a battery charge, DC/DC device or from solar, these devices need to have their maximum charge voltage set to the battery in the parallel mix that has the lowest maximum safe charge voltage level.