Another Battery Question - Montana Owners Club

RMcNeal · 06-22-2020, 08:58 AM

I've been doing some pricing/research on batteries for the rig and would like some advice from those more knowledgeable before I pull the trigger. Let me start by saying we are not full time, but long time, like 60-80% of the time in rig and we NEVER boon dock. I have the residential refrigerator, so keeping it running during travel days and power failure is my primary concern. Our typical travel days do not exceed 4 hours. On some rare occasions we may go as much as 6 hours if absolutely necessary.
I currently have one 12v Road Hawk Predator RV DC27 AGM battery installed by CW when we purchased the unit new last October.
This battery is not keeping up with the refrigerator during very hot travel days even though fully charged. Truck charging circuit is good, I checked. Refrigerator is the new Samsung which lists 3 amps max draw (really? that seems low). The original battery box that came with the unit appears to be just large enough to hold 2 group 27 batteries with no room to spare.
I have narrowed down the battery search to 2 options:
1. 2 12v Group 27 batteries at 90 AH each for about $90 each
2. 2 6v GC2 Golf Cart batteries at 230 AH each for about $130 each
Option 2 will mean replacing the battery box at about another $80-$100.00.
Option 1 means I will have about 90 AH usable at about $1.22 per AH.
Option 2 means I will have about 115 AH usable at about $1.13 per AH.
Both are flooded cell batteries. My converter will not do lithium and the cost is extremely prohibitive anyway, so they were not even considered. AGM batteries appear to be around twice the price, not a deal breaker, but I don't mind the minimal maintenance of the wet cells. I'm pre-wired for solar and generator but have not added either one. I doubt I ever will add solar since we don't boon dock.
Does the 90 or 115 AH seem like enough? Is the extra expense, $140 - $160, really worth around 25 AH of usable battery? Any advice appreciated.

**DQDick** · 06-22-2020, 09:20 AM

My preference is the two golf cart batteries and since I don't bend over well I get AGM's so I don't have to constantly check them.

RMcNeal · 06-22-2020, 09:49 AM

Thanks, DQDick. Any reason why 6v vs 12v? The 6v AGM's are $220.00 each for only 92AH in Group 27 size. That's a big price difference. I read somewhere that AGM batteries can be drawn down 80% without damage as compared to 50% for wet cells. Do you know if this is true?

PeteandJoan · 06-22-2020, 10:49 AM

Quote:

Originally Posted by DQDick

My preference is the two golf cart batteries and since I don't bend over well I get AGM's so I don't have to constantly check them.

X2. I also have a res. fridge and do not boondocks. Last year when I was replacing 2-12v I also asked the same question . It seemed to me that most responses were recommending 2-6v. I have back issues so I bit the bullet and got 2-6v AGM Trojans (217 ah ea.) and a new box without the extra connections thru the lid (weak link IMO). I paid $280 ea. + $75-80 for box. Also installed a cut off switch off the neg post...also recommended here.

RMcNeal · 06-22-2020, 10:54 AM

Thanks, PeteandJoan. I installed a knife style cutoff switch shortly after getting the rig since the convenience center cutoff doesn't actually cut everything off and the other cutoff I have is specifically for the refrigerator inverter. Put it on the negative terminal.
Since you were replacing 2-12v batteries with 2-6v batteries, do you feel like the change was worth it? In other words, do you notice a difference in how long the batteries last compared to the 2-12v batteries you had? I'm having a hard time justifying more than double the cost in my mind.

PeteandJoan · 06-22-2020, 11:16 AM

Quote:

Originally Posted by RMcNeal

Thanks, PeteandJoan. I installed a knife style cutoff switch shortly after getting the rig since the convenience center cutoff doesn't actually cut everything off and the other cutoff I have is specifically for the refrigerator inverter. Put it on the negative terminal.
Since you were replacing 2-12v batteries with 2-6v batteries, do you feel like the change was worth it? In other words, do you notice a difference in how long the batteries last compared to the 2-12v batteries you had? I'm having a hard time justifying more than double the cost in my mind.

I replaced original's when I started having issues on the road....leaving California jacks & slide not working, batteries were 4 yrs old, crumby connections on box lid, bending down into area to service killing my back. So I decided to just do it right and spend the money as most recommend here. No issues since. The statistics & members here say 2-6v do a better job so I went with what made sense to me. I travel about 250-350 miles a day on average and have no problem. I don't monitor the batteries as some do so I can't tell if this setup is actually performing better than old setup, I just knew I needed to replace old ones and get rid of box so I spent the $. My 2-12v worked ....until they didn't. You'll get by with 2-12v but these boys here can tell you exactly why you'll be better off with 2-6v. They'll be here soon.

triplebvalp · 06-22-2020, 11:28 AM

Quote:

Originally Posted by RMcNeal

I currently have one 12v Road Hawk Predator RV DC27 AGM battery installed by CW when we purchased the unit new last October.
This battery is not keeping up with the refrigerator during very hot travel days even though fully charged. Truck charging circuit is good, I checked. Refrigerator is the new Samsung which lists 3 amps max draw (really? that seems low).

Our MHC 295RL has the Samsung Residential Refer and the FW has 2x12v Group 24 wet cell batteries. We traveled 8 hours last Friday (high 80's, lower 90's) without issue. When I backed onto our home parking pad, I disconnected and then checked the battery voltage. It was at 12.6v.

Texan · 06-22-2020, 12:04 PM

2- 6 volt batteries running together will produce more amps than 2- 12 volts. If you are going with 6 volts then the Trojan t-105 6-volt batteries are probably the best if you are going with flooded batteries. 2 12-volt batteries will probably do the job but 2 6-volts will last longer with the higher amps.

jpwhite · 09-02-2020, 09:27 AM

I am need to replace my failed lead acid battery. I do not boondock, but I do want enough dc power to last overnight without plugging in. I am considering a 100 ah AGM battery such as the Duracell WKDC12 or the VMAX MR 127.

For those using AGM batteries, will the Progressive Dynamic 4500 Converter Charger work for them (AGM)?

ChuckS · 09-02-2020, 09:48 AM

Yes the 4500 will work fine

https://www.progressivedyn.com/rv/po...r-4500-series/

RMcNeal · 09-02-2020, 10:11 AM

They are fine for the Lead Acid and AGM batteries and even Gel Cell, but not Lithium Ion of Lithium Phosphate.

twindman · 09-02-2020, 11:48 AM

As for lasting overnite on batteries, it depends. If you are in cold temps and the furnace runs all night, maybe not. The furnace pulls around 10 amps per hour when running. In cold temps my unit runs about 70-80% of the night. So from 8 pm. to 6 am. is 10 hours. So on average of 75%, you use 7.5 amps per hour times 10 hours is 75 ah. Assuming a full charge at 8pm, you will probably make it, but if it isn't fully charged it is touch and go.
Edit: you can guess how I know this!

jpwhite · 09-02-2020, 01:35 PM

Thanks much all for the valuable feedback!

Regarding the PD 4500, I went ahead and ordered the VMAX MR127. It should arrive Friday.

The furnace power usage stats are great, thanks. Getting through the night running the furnace is a lot to hope for on a single battery. I will be happy if I can run the fridge on gas all night. (I actually have the 3120 with RV / Gas fridge). The large Dometic fridge has 12v DC fans running constantly. I ordered a cheap battery monitor to help me understand power usage.

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