Battery Disconect Switch

Sam Spade wrote:

...A battery will provide XX amp hours of energy. Two of the will provide twice that much....

Not quite true. Two batteries in parallel will provide more than twice what the batteries will supply individually. It is an equation figured out by Wilhelm Peukert in 1897.

SoundGuy wrote:
... all because the user chose to install a dual battery disconnect switch.

Sam Spade wrote:
And ALL a waste of time and money.
Discharging only one at a time accomplishes exactly NOTHING.
Charging only one at a time, likewise.

100% incorrect. Run dual 12 volt batteries in parallel and the pair will run down to 50% discharge together, leaving the RV owner stranded without any more battery reserve to fall back on if he wants to preserve the long term durability of the batts by not drawing down beyond that 50% threshold. OTOH, running one down to 50%, then switching over to the 2nd fresh battery not only allows the RV owner to continue camping but offers the opportunity to then recharge the first battery, say by genset, so that once the 2nd battery is down to 50% the first will be ready for service again ... a repeatable cycle for as long as the RV owner may want.

A dual battery switch also offers the choice to run one battery at a time so you're not caught dead in the water without a paddle as just described OR run both together whenever the task at hand may be to power an inverter that in turn is powering a high draw device such as a toaster or coffee maker without excessive voltage drop that could otherwise cause the inverter to go into alarm mode and shut down.

P.S. This ain't my first trip to the Rodeo. I've been in the electronics industry for 50+ years.

Funny about that - 45 yrs in the televison production business as a technical supervisor. You ain't the only one with an electronics background, Sammy. :W

I use the disconnect switch on my trailer. Definitely saves juice.

Had two batteries on the boat and could use battery 1 or 2 or both and could turn both off when not in use. Again, saves juice and I alternated batteries so that I always had a charged battery in reserve on the water.

I have three of these Cole Hersee master disconnect switches. They have a sealed back with O-ring and the contact area is serviceable, rated 310 A continuous. They don't get used much because I can feed and draw off both banks at the same time.

SoundGuy wrote:
Sure ... a Blue Sea m-Series Mini Model #6007 will do exactly what you want.

Maybe this needs to be expanded upon. That switch selects Off, Battery 1, Battery 2, or Both. I saw them all the time when I did boat electronics work.

Gene, stay out of this. Your solution will make the discussion moot, as it is a simple way to accomplish full selectivity, making it possible to do all of the solutions mentioned above. :B

Yep. Get the red switch. You only need about 4 parts.
To make it even easier get the one with just on and off.
Two pre-made cables (local marine store) to parallel the batteries and one red jumper to go from the switch to the main 12v lug.

My only contribution is to point out virtually all boats with dual batteries uses one of the dual battery switches shown above, so it must be possible and usually for weight distribution boat batteries on on opposites about 6' apart.....

coolbreeze01 wrote:
I alternated batteries so that I always had a charged battery in reserve on the water.

This is not a boat forum.

IF you have access to a reasonably good charging method, like shore power or a generator, there is NO real advantage to using one battery while charging another. The charging source does a fine job of providing power to USE while it also charges the weak batteries.

Two batteries connected together last at least twice as long and even if run down to almost totally flat, the system will have usable voltage again a few seconds after a charging source is attached, assuming that it has sufficient capacity.

IF YOU HAVE A GOOD CHARGING SOURCE, THERE IS NO ADVANTAGE TO USING YOUR TWO BATTERIES ONE AT A TIME. NONE.

Sam Spade wrote:
IF you have access to a reasonably good charging method, like shore power or a generator, there is NO real advantage to using one battery while charging another. The charging source does a fine job of providing power to USE while it also charges the weak batteries.

Charging a typical 12 volt battery like a G27 drawn down to 50% would take a genet like the ubiquitous Honda EU2000i approximately 3 hrs to restore battery charge to ~ 90%. Charging two batteries in parallel would obviously take just that much longer. :R

Sam Spade wrote:
IF YOU HAVE A GOOD CHARGING SOURCE, THERE IS NO ADVANTAGE TO USING YOUR TWO BATTERIES ONE AT A TIME. NONE.

Just like in a schoolyard - if you can't get your way just yell and maybe someone will pay attention. :S