Replacing AGM 75wh sealed battery with two regular (unsealed) 12v 100wh batteries in my ATC Bobcat.

[JeffWright]

Hey guys,
A friend upgraded his 12volt system recently to a 6 volt system and offered to give me his two almost new deep cycle 12v 100wh batteries.

I have a 75wh AGM that's about a year old. I've got a 3 way fridge that I only run on battery when I'm traveling. If I am running errands on the way out of town and leave the fridge on battery for more than an hour or two in the parking lot I get into dangerous voltage territory and my isolator won't charge it. I've showed up to a campsite after driving for a couple hours and started my trip at 50% voltage.

I know it's my fault for not switching to propane every chance I can get but I'd really like to take some of the user error out of the equation so I'd like to add more watt hours. I priced adding another 75 wh AGM and it was about $250 for the one I already have (I know you are supposed to buy them at the same time but mine is only a year old so I am not worrying about it).

I know AGM batteries are much less of a pain in the ass but what would the drawbacks be of using the deep cycle batteries other than maintenance? My system is located under my rollover couch. Would I need something like this for venting:

http://www.adventurerv.net/vented-battery-box-large-white-p-4085.html?gclid=CN-X1-DmjM8CFQZufgodSBoA0w&utm_campaign=partsfeed_ppc&utm_medium=cpc&utm_source=Froogle

Right now I have more time than money so I'd rather go cheaper and have more money for adventuring.

Thanks!

 

[Trailbob]

My first FWC was a 1999 Hawk that didn't come with a battery. Back then, they put the extra battery in the truck bed, not the camper. I added a group 24 flooded battery under the dinette seat, and vented the battery box outside, similar to your link. It worked fine for many years until I sold the camper.

So, I think you "could" do it, but not sure you "should" do it. As mentioned above, I ran a single group 24 battery (75ah) for around 9 years in my first FWC, and 4 years in my second FWC. I only changed to two group 24 (75ah) AGMs last year when I bought an ARB fridge to use in addition to my 3 way fridge.

You already have 150ahs available with your current set up. If you increase it by 50ahs by changing to two 100ah batteries, you will gain another 25 usable AHs. I have not run the numbers, but if you currently arrive at camp with 50% discharged batteries, with the bigger batteries you would probably arrive with 30 or 40% discharged batteries. This would be way to low for me, I like to arrive at or near 100%.

Another consideration would be trading the advantages of AGMs for the disadvantages of flood cell batteries.

You might reconsider how you travel with your 3 way fridge. A 3 way fridge on 12V is a huge drain. Sometimes I will do it on a long freeway trip (to save propane), but I monitor batteries on the Trimetric at every stop. Normally I travel with the fridge on propane, but I understand that others do not like doing this. An option might be to pre-cool your fridge, and put jugs of ice in it while travelling.

So, a long winded way to say it could be done, just not sure it should be.

 

[JeffWright]

My first FWC was a 1999 Hawk that didn't come with a battery. Back then, they put the extra battery in the truck bed, not the camper. I added a group 24 flooded battery under the dinette seat, and vented the battery box outside, similar to your link. It worked fine for many years until I sold the camper.

So, I think you "could" do it, but not sure you "should" do it. As mentioned above, I ran a single group 24 battery (75ah) for around 9 years in my first FWC, and 4 years in my second FWC. I only changed to two group 24 (75ah) AGMs last year when I bought an ARB fridge to use in addition to my 3 way fridge.

You already have 150ahs available with your current set up. If you increase it by 50ahs by changing to two 100ah batteries, you will gain another 25 usable AHs. I have not run the numbers, but if you currently arrive at camp with 50% discharged batteries, with the bigger batteries you would probably arrive with 30 or 40% discharged batteries. This would be way to low for me, I like to arrive at or near 100%.

Another consideration would be trading the advantages of AGMs for the disadvantages of flood cell batteries.

You might reconsider how you travel with your 3 way fridge. A 3 way fridge on 12V is a huge drain. Sometimes I will do it on a long freeway trip (to save propane), but I monitor batteries on the Trimetric at every stop. Normally I travel with the fridge on propane, but I understand that others do not like doing this. An option might be to pre-cool your fridge, and put jugs of ice in it while travelling.

So, a long winded way to say it could be done, just not sure it should be.

Hi Trail Bob, thanks for getting back to me and for the feedback! It might have been a bit unclear but my friend offered me two 100 wh batteries so I'd have 200wh of total juice as compared to the 75 wh I have now. I haven't tried using the propane when on the road. I was under the impression that it would blow the pilot light out. I also pre cool the fridge with 120v which helps me a ton. Heading into the winter I want to make sure I have enough juice left for the furnace (obviously the fridge will be easier to keep cool too). Maybe I'll give the propane on the road a try and see how I can do.

 

[JaSAn]

I have a 75wh AGM that's about a year old . . . I've showed up to a campsite after driving for a couple hours and started my trip at 50% voltage.
. . .
I priced adding another 75 wh AGM and it was about $250 for the one I already have (I know you are supposed to buy them at the same time but mine is only a year old so I am not worrying about it).
. . .
I know AGM batteries are much less of a pain in the ass but what would the drawbacks be of using the deep cycle batteries other than maintenance? My system is located under my rollover couch.

If your friends 12V batteries are true deep cycle, I would grab them (should weigh > 100 lbs each). If your current battery has been run to lower than 50% a number of times and hasn't been recharged quickly it probably is getting well sulfated (less capacity, shorter life). Connecting a new battery to it would shorten the life of the new one.

As for FLA being a pain in the ass; it hasn't been for me. I check water level before every trip, check specific gravity twice a year (something you can't do with AGM), equalize twice a year (harder to do with AGM). Venting is a one time mod.

The two 12V/100AH batteries will give you 100AH usable vs. 37AH usable you currently have. You can't beat free.

As for leaving the frig on propane while driving: I have friends that do this with no problems. You just have to remember to switch to 12V while fueling. There is a post i read (I think on this site) about making a shield for the flame if you have a problem with it staying lit while driving.

jim

 

[craig333]

Might try this for the 3way.

http://www.wanderthewest.com/forum/topic/1111-tech-tip-auto-relighter-for-propane-refrigerators/?hl=relighter

 

[JeffWright]

If your friends 12V batteries are true deep cycle, I would grab them (should weigh > 100 lbs each). If your current battery has been run to lower than 50% a number of times and hasn't been recharged quickly it probably is getting well sulfated (less capacity, shorter life). Connecting a new battery to it would shorten the life of the new one.

As for FLA being a pain in the ass; it hasn't been for me. I check water level before every trip, check specific gravity twice a year (something you can't do with AGM), equalize twice a year (harder to do with AGM). Venting is a one time mod.

The two 12V/100AH batteries will give you 100AH usable vs. 37AH usable you currently have. You can't beat free.

As for leaving the frig on propane while driving: I have friends that do this with no problems. You just have to remember to switch to 12V while fueling. There is a post i read (I think on this site) about making a shield for the flame if you have a problem with it staying lit while driving.

jim

Thanks Jasan, good advice. They definitely don't weigh a hundred pounds each. Probably 50lbs each.

 

[JeffWright]

Might try this for the 3way.

http://www.wanderthewest.com/forum/topic/1111-tech-tip-auto-relighter-for-propane-refrigerators/?hl=relighter

Thats really cool! I haven't seen them.