How is the second battery electrically connected?Just paralleled? Do you add a disconnect for each for quicker charging one at a time?Thinking another battery would be better for boondocking.

Boomerweps wrote:How is the second battery electrically connected?Just paralleled? Do you add a disconnect for each for quicker charging one at a time?Thinking another battery would be better for boondocking.Connect dual 12 volt batteries like this ...... BUT it's not advised to connect batteries in parallel at all if your current one is several years old as it's characteristics will have changed sufficiently that it will draw down the new one and allow neither to charge properly. If your current battery is relatively new then I would do it but only if the second new battery was the same make / size as the original. However, all this raises the more important question - do you have a charger suitable for properly charging 2 deep cycle batteries? :@

Use the diagram shown above. Note that you get more than twice the time at the same amps draw by having that second battery used together. So don't use them one at a time. (Peukert works for you!) Charging them both back at once takes no longer, and even might help if you have one of those WFCOs that has a hard time getting to 14.4 instead of staying at 13.6. (Doing two lowers your charging rate for the same amps perhaps letting it see the 13.2 trigger)

This is what is balanced and best for twin twelve volt batteries.As it often doesn't cost a dime more to do this, I think it is worth the trouble.If you wish to understand the "why" surf here:correctly interconnecting multiple twelve volt batteriesOthers may say it doesn't matter--but unless there is a compelling reason to not optimize charging and discharging why not do it the best possible way?

BFL13 wrote:Use the diagram shown above. Note that you get more than twice the time at the same amps draw by having that second battery used together. So don't use them one at a time. (Peukert works for you!)OTOH if the OP's original battery has been in use for awhile but he still wants the benefit of having two batteries available for dry camping then he should use them separately to avoid the old original from degrading the newly purchased battery. He can easily accomplish this by wiring the batteries with a dual battery disconnect switch such as the Blue Sea m-Series 6007.

Connecting a second 12VDC battery | Good Sam Community

22 Replies

pianotuna
Nomad III
May 09, 2018
Hi,

Since you plan to boondock you may wish to get an inverter/charger. The best of those outshine any converter currently available.

Rail Dawg wrote:
Excellent info!

Just learned a few things from you and I appreciate that.

Didn't realize the drop to 12 volts provides 330 amps of power!

Think I'll invest in a better converter.

Appreciate the help.
SoundGuy
Explorer
May 09, 2018
pianotuna wrote:
While recharging using solar is the nearest thing to a free lunch you may every find, having an excellent device to charge the battery bank is definitely NOT moot, when powered by a generator.

I never said it was, rather I said having a good converter IS moot if one always charges while camping with solar and not a genset. That said, the OP will eventually go home and presuming he keeps the trailer where he can plug into shore power he would benefit from upgrading his WFCO converter which never achieves it's advertised 14.4 volt bulk charge rate for something like a Progressive Dynamics 9200 series that will. I myself turned off my own WFCO and instead use a stand alone CTEK charger which does deliver to the battery a proper 14.4 volt bulk charge.
Rail_Dawg
Explorer
May 09, 2018
Excellent info!

Just learned a few things from you and I appreciate that.

Didn't realize the drop to 12 volts provides 330 amps of power!

Think I'll invest in a better converter.

Appreciate the help.
pianotuna
Nomad III
May 09, 2018
Hi Rail Dawg,

33 amps @ 120 volts translates to 330 amps @ 12 volts.

The WFCO is famous for never ever going into bulk charging mode, so it takes many many hours of generator time to recharge the battery bank (if it ever gets there--perhaps 168 hours might get close).

The PD with wizard is easy to "set" for 14.4 volts and may charge the bank much faster than the WFCO.

However, no one who does not absolutely have to tries to recharge to 100% using a generator--it simply takes too long.

The reason for this is the "acceptance" rate on a lead acid jar drops to 12.5 amps @ 85% state of charge. The closer to 100% the lower the charge rate.

There are a couple of other excellent converters such as the IOTA (with genius), and iirc the Boondocker. There are other devices such as inverter chargers that are even more effective and more programmable. For example, my Magnum can "push" up to 127 amps into the bank.

While recharging using solar is the nearest thing to a free lunch you may every find, having an excellent device to charge the battery bank is definitely NOT moot, when powered by a generator.

Rail Dawg wrote:
My generator while 8000 watts only puts out 33 amps on each leg.

If my WFCO charger is rated at 35 amps will there be any benefit to going with a better converter like the Progressive Dynamics?
Rail_Dawg
Explorer
May 09, 2018
SoundGuy wrote:

Progressive Dynamics ... but which converter you have is moot if you always charge with solar. If however you intend to use that genset then yeah, upgrading your converter would be a wise investment.

My generator while 8000 watts only puts out 33 amps on each leg.

If my WFCO charger is rated at 35 amps will there be any benefit to going with a better converter like the Progressive Dynamics?
SoundGuy
Explorer
May 09, 2018
Rail Dawg wrote:
Am wondering if my setup is good for boondocking or do I need a better converter like a Precision Dynamics to replace the WFCO.

I do have a good generator when out in the desert.

Progressive Dynamics ... but which converter you have is moot if you always charge with solar. If however you intend to use that genset then yeah, upgrading your converter would be a wise investment.
red31
Explorer
May 09, 2018
Boomerweps wrote:

I keep looking at solar but I haven't even taken the camper out of the yard, yet ;)

switches etal do not charge or maintain batteries.
total disconnect from parasite loads is good.
boon-dockers need fully charged batteries to start with and charge/maintenance between trips.

Solar works in the yard! (if there is sun).
BFL13
Explorer II
May 08, 2018
When boondocking the converter is only able to be used with your generator. (no shore power!) So it is all solar, and your controller can meet the Trojan specs.

No need to change the converter if you don't use it anyway.

Even if the WFCO did do its 14.4v, the 35 amper isn't going to make much of a dent in a pair of 6s in a couple hours of gen time. You need to consider the big picture scenarios for when and where and for how long you camp to figure out what would be your best set-up for likely need for gen time and availability of enough sunshine.
Rail_Dawg
Explorer
May 08, 2018
SoundGuy wrote:
You also really need to investigate just which converter is in this trailer 'cause if it's a WFCO you'd probably want to replace it right from the get go ... good enough for those who normally camp on electric sites but certainly far less than ideal for those who dry camp, especially those with $$$ invested in substantial battery reserve. ;)

I keep hearing about replacing the WFCO.

Got a new rig with the WFCO 35-amp.

Just replaced dealer battery with 2 Trojan T105 AGM’s.

Also installed 435 watt solar panel with Victron Solar MPPT 100/35.

Am wondering if my setup is good for boondocking or do I need a better converter like a Precision Dynamics to replace the WFCO.

I do have a good generator when out in the desert.

Thanks.
pianotuna
Nomad III
May 08, 2018
Hi,

This may help you with solar:

https://freecampsites.net/adding-solar/

Boomerweps wrote:
I keep looking at solar but I haven't even taken the camper out of the yard, yet ;)