second battery to charge off the engine like the original?

RoyB wrote:
I am planning on using a SMART RELAY here manf by BLUE SEA called the SI-ACR relay in an upcoming battery project. Another popular smart relay is called a BATTERY SEPARATOR manf by SURE Power Industries....

All the OP would need is a continuous duty solenoid. People have used them for this purpose successfully for ages.
http://www.amazon.com/Continuous-Duty-Solenoid-80AMP-12V/dp/B0050I94XG

enblethen wrote:
A group 24 or 27 would last for a night or two depending on use. 2 6 volt batteries wired in series would give more.

...

1. 2 x grp 31 dual purpose batteries v.s. 2 x 6V GCs is a much fairer and more equal comparison based on more equal weight and Amphours.

2. The same goes to battery type. 12Vs are hybrid dual purpose, therefor giving a good compromise between low and high draws. GCs are deep cycle only and not designed for high draws.

It depends! What is the run time for a 1500W microwave with 2 x 6V GCs?

HTH;
John

Cant seem to find any of that info or if it has a charge relay. Hmm. Ill try 2 6volt batteries and see how it does. Maybe ill just add a 3rd later on if desired. Thanks

I have gotten the GC 2 batteries from Costco. About $80 each.
Four batteries will extend use time but will also increase the recharge time.
I would check your alternator to see what capacity it is and it's condition.

Ok thank you. Which 6 volt batteries are best and what if i did.4?

A group 24 or 27 would last for a night or two depending on use. 2 6 volt batteries wired in series would give more.
Look in your owner's manual to see if it has a charge relay for trailer towing. This relay would serve the same as RoyB's after market.
Mounting batteries in the rear you would need to use some prewtty healthy wire to prevent voltage drop no matter which battery(ies) you choose. I would be thinking around a #4. Fuse at 30 amp near your existing battery.

It is an 03 dodge van non extended. 5.9ltr. No room in hood, possibly underneath the rear bumper area. Thank you both for the info so far. The si acr thing looks good. But what kind of battery should i be trying to use to run all of this equipment?

I am planning on using a SMART RELAY here manf by BLUE SEA called the SI-ACR relay in an upcoming battery project. Another popular smart relay is called a BATTERY SEPARATOR manf by SURE Power Industries. These both pretty much do the same thing.


In todays world of charging deep cycle batteries you cannot use the old days DIODE BASED battery ISOLATORS. These devices uses high current DIODES which will drop your DC VOLTAGE by .7VDC going thru them. In the older days this was not a problem but todays DEEP CYCLE batteries require 14.4VDC to properly re-charge the batteries in a short three hour time period. If you subtract 14.4VDC-,7VDC voltage drop then you only get 13.7VDC to charge your deep cycle batteries, This will take around 12-13 hours to re-charge your deep cycle battery to be able to use it immediate again.

This is why you should install SMART RELAYS verses DIODE BASED ISOLATORs like shown above which will parallel batteries to your normal start battery when charging is needed. This method will keep your down-leg batteries re-charged and never discharge your start battery setup. It does this automatically...

Read up on BLUE SEA SI-ACR charging circuits at their web site - good info there to give you some ideas on what you might need to install.. Same goes for the SURE POWER INDUSTRIES website. Lots of good application info there as well.

Roy Ken

It should be very easy to wire in a second battery. Some vans and trucks come with a circuit for this pupose.
Make and model of van would be helpful.
Problem is locating the battery so it is vented to the outside as it is not good to have battery gases inside living areas. Yes, you could get sealed batteries such as AGMs but they are costly.
Some rigs have enough room to put under the hood oppoite of the existing battery. You have to look at your rig.