feedback on dual battery system design?

[Umbrarian]

Which would show the battery produces 12V and tell you nothing about it being connected to the car. Take it one step further disconnect both leads from the battery remove it from the car, put it your garage and then put a test light on the terminals - and the test light will light up, telling you precisely nothing about its connection to the car. Instead, leave the battery in the car, disconnect the negative cable form the battery, and then use your test light from anything in the car (ground, alternator, really anything) to either terminal of the battery and it won't light up, coz the battery is not connected.

Your limited experience with a handful of cars has caused you to generalize that all cars have a single battery, a single terminal, and are connected all the same. This is not the real world. Couple this with your imprecise statements "your car will run just fine without a battery", and "you car would likely run without the battery at all" when you really meant it does have a battery, it just might not be working correctly, and I see the source of your confusion. My bad for not reading through your errors.

 

[martnH]

It's a good idea. I never thought of a back up battery.....But it's actually a good idea

But your setup suggest you will need a cranking plus deep cycle battery as the main battery.And also a cranking (high CCA) battery as a backup.

I think it will work out good for you and the way to charge the backup battery, I think there is only one way and that's to use a dc-dc charger. This will prioritise charging your backup battery.

Sent from my LG-H870DS using Tapatalk