Following your recent explanation of the benefits of fitting two batteries, I am considering doing that. Is it best to connect them separately or what? JNK
There are three main ways to wire up a second battery.
The way that is likely to be most useful to most motorists is to connect them both “in parallel,” so they both do the same job as one.
That way their voltage remains correct at 12V, but their storage capacity and discharge rate are increased (doubled) and the work each one has to do is reduced.
If your motoring patterns remain unchanged, both batteries will remain more fully charged, and every discharge load (especially for starting) on each battery will be halved. They are both likely to last a lot longer. And if one fails, the other will continue to meet the vehicle’s electrical requirements.
A second way is to have two batteries, each connected to all electrical functions, but to use only one at a time, with a change-over switch allowing you to select which one.
This set-up may be preferable if the vehicle goes on safari and uses the batteries for electrical power in camp (a portable fridge, lights etc). If one becomes heavily discharged (or fails) the other is there as standby and extra capacity and to get the car started to recharge them both.
A third option is to wire each battery to different electrical functions – usually, one is connected to the starter motor only and the other is connected to everything else.
This can be especially reassuring in remote areas, knowing that if the “everything else” battery is deeply discharged there is another fully charged battery to get the vehicle (and hence the charging system) going again.
You can, of course, simply carry a fully-charged spare battery in your luggage; but why not make it do some work as well?
