Two Similar 12V battery in parallel and other questions

[Fortkentdad]

Well I just bought a second battery for my RV. My other battery is only a couple of months old so both are new this year. The one battery didn't make it through an unplugged camping weekend so we decided another was needed.

I'm not sure if I should hook them together as one bank in parallel or just swap the connecting cables when one is less than 1/4 full on the battery meter in the trailer.

We are only weekenders - and maybe a week or two here and there. Not full timers at all. And when we camp we are not running a lot of power.

One of my concerns is the batteries are not identical.

One is Canadian Energy's P27 MHC (CDN Energey P27 MHC) The other is an Everstart from Walmart it is the 27DC-850N apparently by Johnson Controls (CDN made)

Both are 27 "RV MARINE DEEP CYCLE" batteries. Both cost about the same ($111 & $119)

But not all the ratings are not exactly the same. The Everstart's MCA is 850 on and only 750 on the "Canadian Energy" battery

The Cold Crank on the Everystart is 675 vs only 600 on the CDN Energy battery.

Both have a "RC" of 180.

The Everystart lists its AMP/H as 120 the CDN Energy does not list AMP/H on the battery or website

As my converter is caput and I have not got around to replacing it I run off of my batteries all the time. I was using a old 6 amp trickle charger to charge up the battery but just bought a Genius Mini 2 charger. It is a waterproof unit and a "smart charger" indeed their marketing gimmick is "wicked smart". Each battery is connected to one of the wires from this charger 100% of the time. It is intended to be mounted on the RV (or boat or whatever) and left on all the time. It does say it is for RV's. The Mini-2 is really 2 4 amp chargers combined in one unit designed to keep two batteries charged. Genius GEN Mini2

I've emailed the manufacture for clarification on whether I should keep both batteries hooked directly to the the charger when they are hooked up in parallel. Or when I connect the two batteries does that make it like one big battery? I am concerned as the GENmini which I bought is intended for a battery with a max capacity of 120 amp/hr. If I hooked the two together are they then considered one battery with 200-ish amp/hrs?

I also have two Coleman 40W Solar systems - each has its own 7 amp charge controller. I will also be hooking these up to the batteries. I can hook them up together (parallel) to have 80w running through one of the controllers or keep them separate and charge each battery independently. Not sure which is the best approach.

SO - connect them in parallel OR keep them separate and just manual swap the connections when the battery charge is getting low. (I suppose there is some sort of switch that could be installed to make this easier).

Besides the inconvenience of switching the cables is there a downside to not hooking them up as one parallel bank? IF isolated that would ensure that we are never totally out of power. (been there done that didn't like hand cranking the slides).

I also wonder about the need to replace our converter. It's $300 for the WFCO OEM 55amp replacement $400 if I upgrade to Progressive Dynamic's unit. (CDN prices) What do I gain? Besides not using the batteries when I have shore power. If I keep them charged what is the difference?

David

[tenbear]

Lots of good advice re batteries. You might also consider reducing your battery power drain. If you haven't already switched over to LED lighting you might consider that. Switching to LEDs can reduce your lighting power drain by about 80%.

[Almot]

If they are both of the same specs, i.e. same charging setpoints - connect them in parallel. Preferably in a balanced manner like Pianotuna described.

And, I would not trust a trailer OEM wall meter to check the battery charge.

Definitely, I would avoid discharging it down to 1/4 of full capacity like you described. It's good to know that batteries prices can be that low, still there is no reason to treat them badly.

[wa8yxm]

I have seen many people yammer about the need for all batteries in a bank to be IDENTICAL (Same age, size, make, model Bla Bla Bla)

For batteries in series,, This is true of each string.. (IE if you have a 5 cell Mag-Light flashlight you always replace all 5 batteries at the same time)

But for batteries in parallel.. You can mix and match so long as they are the same voltage and chemistry.

Mixing AGM, Flooded wet and Maintenance Free, .. Well, I have done it, with no problems but I can not recommend it (or against it)

But mixing two maintenance free (older and newer or bigger and smaller) no problem.

[westend]

My take: Connect both batteries together in parallel, having a master disconnect switch that interrupts the batteries from any 12V except for the break-away system.
If you have solar, connect it and leave it connected for storage considerations. Replacing the converter would obviate the use of a trickle charger as the newer converters will have the same function. The converter will also offer the capability of charging the batteries in a shorter time, something that is very important to those with generators. About the only thing "wicked" with the Genius charger is that the "boost" function operates at 16V (how many amps is unknown). That would be helpful to equalize an untended battery.

The OP doesn't state what's wrong with the original WFCO converter but I wouldn't replace it with the same as there are many testimonials as to the superiority of the PD converters.

It sounds like the SOC of the battery has been a guess (battery is dead on occasion). This is a bad situation as even a hybrid marine battery will eventually have an early death from discharging it to less than 12V, especially if no immediate manner of charging is present. A battery monitor, an inexpensive 12V panel mount gauge, or a hand-held meter will indicate the state of charge so that early battery death is not imminent.

[RJsfishin]

The 4655 is the correct replacement, but expensive, only because it fits where the old one was. It is a price rip in reality.
The 9245 or 9260 are the same converters, except they are stand alone converters similar to a battery charger, and they connect just like a battery charger. If you have the space near your electrical panel, or near the batteries, I would prefer to go w/ the stand alone, and save the money at the same time. And you would leave the existing converter where it is. The 9260 (bigger amps, smaller size) just mite fit in place of the Wfco (have to check)

But if you drive in and say fix it, the 4655 it will be,

[Fortkentdad]

RJsfishin wrote:
To answer some of the questions,.....hook them in parallel,.....less chance you will run them down beyond the 50% rule.
If you use more power than 50%, charge them,...one way or another, even if connecting jumper cables from TV.

Then, replace the converter, one way or the other. A PD9245 can be had for around $129 off ebay. and it usually includes the remote pendant to control the charging stages.
And last of all, a 1000 watt generator to power the PD,.......or a couple hundred watts of solar to give the batteries a fighting chance of living a longer life.

RE: The PD9245 is not the one Progressive Dynamic recommends as a replacement for the WFCO 8955 which I'm replacing - that one is the PD4655. Does that matter or will any converter work?

That model is about $80 less than the PD4655 which is the PD recommended replacement. Off eBay I can get the PD recommended replacement unit - PD4655 for about $250+$60 - or about $100 more than the PD9245. Amazon.ca has them for similar prices and better warranty service. Or I can get a WFCO 8955 for about $175 from Amazon.ca

Considerably less than RV shops around here.

[calamus]

I got 2 group 27s Trolling motor batteries from a battery dealer here for $170. They are Crown batteries

[Fortkentdad]

Bumpyroad wrote:
so you bought a 120 AH battery size 27 at walmart for $119.00 canadian?
think I'll head down to my local store on Monday.
bumpy

Actually the Walmart one was $111 - the other one was $119

[RJsfishin]

To answer some of the questions,.....hook them in parallel,.....less chance you will run them down beyond the 50% rule.
If you use more power than 50%, charge them,...one way or another, even if connecting jumper cables from TV.

Then, replace the converter, one way or the other. A PD9245 can be had for around $129 off ebay. and it usually includes the remote pendant to control the charging stages.
And last of all, a 1000 watt generator to power the PD,.......or a couple hundred watts of solar to give the batteries a fighting chance of living a longer life.

[Bumpyroad]

so you bought a 120 AH battery size 27 at walmart for $119.00 canadian?
think I'll head down to my local store on Monday.
bumpy

[pianotuna]

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 batteries

Others 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?