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I"m in the planning stages to make my new PM 3500 into a stealth camper in time for my retirement. I have several floorplans in mind, but I cannot proceed until I know where to place the four 300 amp AGM batteries. They could be series /parallel two each, side by side or all four in a row. They weigh 90 pounds each. Can I locate them next to the inside walls, or will I need to plan on a more central location, which of course takes up valuable space? I am concerned about 400 pounds of weight affecting steering and stability if the batteries are close to the wall. Can the PM's suspension handle the uneven payload?
 

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Hi JagdPaul,

Welcome and good luck with your camper. I want to build one or have Sportsmobile build one for our retirement too, but I have another ten years to go and the wife has more pressing priorities for now so we will rent Sprinter campervans for a few years.
Have you considered installing lithium batteries for power? I have a 16KW pack in my mitsubishi miev and I love lithium batteries. They are so much lighter than lead and they last many times longer. The price is pretty reasonable too. Actually, in the long run I think they are more cost effective.
 

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I"m in the planning stages to make my new PM 3500 into a stealth camper in time for my retirement. I have several floorplans in mind, but I cannot proceed until I know where to place the four 300 amp AGM batteries. They could be series /parallel two each, side by side or all four in a row. They weigh 90 pounds each. Can I locate them next to the inside walls, or will I need to plan on a more central location, which of course takes up valuable space? I am concerned about 400 pounds of weight affecting steering and stability if the batteries are close to the wall. Can the PM's suspension handle the uneven payload?
Have you considered under the floor? That would increase interior space and lower the center of gravity. On a FWD ProMaster it should be possible to place then in center of van, plus also forward or back as desired to provide optimum weight distribution.

I've seen a few sealed batteries inside RVs, but most RVs (including Class Bs) I've ever seen had them outside. There are downsides to that -- like possible extreme temperatures and less access -- but it seems to be the norm. Some are mounted on trays to improve access.

Personally I'd try to keep deep-cycle house batteries out of van unless they were lithium. Even then I'd place then under floor to gain space.
 

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Thanks for the replys. These are excellent ideas I did not consider. The lithium batteries are superior in every way except (gulp) price. But I do have $40,000 already invested in the PM, so what the ****. The positioning of the batteries underneath the floor sounds good and is an idea I will be definitely look into. Thanks
 

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I recommend researching possible safety issues when thinking of placing batteries inside living space. If something goes wrong with charging system or with a battery, it could put occupants in greater danger than if mounted outside where they can vent.

Lithium batteries are very different and may not have similar issues. I haven't looked into them as much because they are so expensive for the same energy capacity, although they do save much weight and should last much longer. I just hope costs come down some.
 

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How I see it if you need a battery for serious heavy duty use in your $40k+ Promaster, you might as well spend hundreds extra just go to lithium ion. It's the obvious choice when going for a superior battery
 

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I think for the amount of batteries he's planning on, the cost difference is in the $1000s.

As I read his initial post, it seems he is planning on four 300 amp-hour 6-volt batteries. When connected in series and parallel as described, he'll end up with 600 amp-hours at 12 volts. If not what was meant, please correct me.

Anyway, the lithium batteries I was looking at were in the range of $1300 for each 100 amp-hour 12 volt battery. Six would cost almost $8000. If bought in larger units, like two 300 amp-hour 12 volt units the cost was reduced to about $7000.

Compared to cheaper AGM batteries that could be over $5000 more. It may very well be worth it for some, but it is expensive.
 

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Don't lithium batteries require a special charger as well? That would be critical for both a solar component, and the converter charging from the generator, engine, or shore power.
 

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"Don't lithium batteries require a special charger?"

Yes they do. Lithium cells have a different cell voltage than lead acid cells (3.6 or 3.7v/cell for lithium ion vs 2.1v/cell). Lithium cells require a constant current/constant voltage charge process which may be used with lead acid batteries as well, but with different rates and voltage end points. You do NOT want to overcharge or over discharge a lithium battery, or exceed recommended charge current rates as it will be ruined and may result in unsafe conditions. For that reason special chargers are required as is a battery management interface. All power tools with lithium packs have these. My RC planes use 3-cell, 11.1v soft packs which have low voltage cut off set no less than 3.0v/cell by the speed control, and balanced charging done with a digital charger and balancing board. The power to weight ratio is amazing, but it's a bit of a pain having to babysit the battery while it's charging in a flame resistant bag which is in a metal tool box just in case something goes wrong. These same batteries are stored in those same containers because things can happen, though I think there's a degree of accountability also to be placed on handling and usage abuse.
 

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Battery safety inside Promaster

Is there in fact a battery that would be safe in the cargo portion of the van? The engine battery is in the floor below the driver--is that considered safe? I want to install a secondary "house" battery for a few things like fan and lights when the van motor is off at night. Seems like the area under the drivers seat would be great for a small battery. What sort of battery do I need to run a fan and lights for a few hours at night that would be small and safe?
 

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"Don't lithium batteries require a special charger?"

Yes they do. Lithium cells have a different cell voltage than lead acid cells (3.6 or 3.7v/cell for lithium ion vs 2.1v/cell). Lithium cells require a constant current/constant voltage charge process which may be used with lead acid batteries as well, but with different rates and voltage end points. You do NOT want to overcharge or over discharge a lithium battery, or exceed recommended charge current rates as it will be ruined and may result in unsafe conditions. For that reason special chargers are required as is a battery management interface. All power tools with lithium packs have these. My RC planes use 3-cell, 11.1v soft packs which have low voltage cut off set no less than 3.0v/cell by the speed control, and balanced charging done with a digital charger and balancing board. The power to weight ratio is amazing, but it's a bit of a pain having to babysit the battery while it's charging in a flame resistant bag which is in a metal tool box just in case something goes wrong. These same batteries are stored in those same containers because things can happen, though I think there's a degree of accountability also to be placed on handling and usage abuse.
X2
Houses have burned down from lipos ( I am into rc helicopters).
 

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I've been building motorcycle batteries using Dewalt battery packs up until everyone got the same idea and drove the prices out of sight. 4 cells in one of their packs will start a car. If you have any bad batteries, don't throw them away as usually only one cell is bad.
 

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Is there in fact a battery that would be safe in the cargo portion of the van? The engine battery is in the floor below the driver--is that considered safe? I want to install a secondary "house" battery for a few things like fan and lights when the van motor is off at night. Seems like the area under the drivers seat would be great for a small battery. What sort of battery do I need to run a fan and lights for a few hours at night that would be small and safe?
Needed battery size depends on your planned load and duration, which can vary all over the map. LED lights for example use less power, but you need to define how many you will install and use. Fans also vary in size and current draw. And by a few hours do you mean 2 hours or could it sometimes be 3 or 4 or maybe even longer? Basically it comes down to how much energy needs to be stored and what size battery can deliver that much energy. If you will be using 12 volts to keep it all simpler then a simpler way to estimate battery size is by adding up "amps X time", normally referred to as battery Amp-hours. Keep in mind that battery ratings change with discharge rate, so it's not a constant number like many people wrongly assume.

As to placement I personally wouldn't install a battery inside. Some auto manufacturers have installed batteries under seats or in trunks, but for most part they go outside. Factory auxiliary batteries normally go outside too.
 

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Thanks Chance--who should I search out to do the work of installing auxiliary battery--auto shop, RV shop, stereo etc. installers?
 

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The Promasters battery is in the floor between the front seats! Personally, although everyone recommends against it, I would have no problem putting the battery inside the van. My Sprinted had two 6 volt lead acid golf cart batteries inside for ten years with never a problem. Perhaps if you were to close it up tightly and store it for a while it could cause a problem but mostly I think it's more of a case of not enough to worry about. I'll most certainly will be putting my house battery inside when I get around to it with no worries.
 

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The Promasters battery is in the floor between the front seats! Personally, although everyone recommends against it, I would have no problem putting the battery inside the van. My Sprinted had two 6 volt lead acid golf cart batteries inside for ten years with never a problem. Perhaps if you were to close it up tightly and store it for a while it could cause a problem but mostly I think it's more of a case of not enough to worry about. I'll most certainly will be putting my house battery inside when I get around to it with no worries.
While it hasn't happened to me personally, I've been around a couple of batteries that exploded under different conditions. They were preventable accidents but they occurred regardless. In both cases battery gases ignited from a nearby spark and detonated. Both events startled everyone that was close. It's nothing I'd want inside my RV.

Corrosion can also be an issue, although that can happen inside or out. Just less likely to do damage when outside in my opinion.
 

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I'm sure you're right but I still would worry about it in the slightest. On the other hand, I wouldn't even consider having propane in either my house or van for what it's worth (which isn't much)
 

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Thanks Chance--who should I search out to do the work of installing auxiliary battery--auto shop, RV shop, stereo etc. installers?
I can't say for sure who would do the best work -- I have a technical background and do that type of work myself so I've never looked into having it done for me. I expect much would come down to luck on getting a good installer.

Having said that, I would probably do lots of research (charging and discharging battery without affecting vehicle is probably more important than battery location and/or size) and would then contact Class B RV converters/builders for pricing if you have any close by. It's probably more expensive that way but I'd personally feel better about them knowing what they are doing.

You will probably want to charge battery off vehicle but at same time keep from draining your starting battery when using lights and fan. That can be done in many ways from simple manual switches to fully automated system. There is a good write-up on options in the Sportsmobile forum. I think it's under electrical section as a sticky thread.
 

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I'm sure you're right but I still would worry about it in the slightest. On the other hand, I wouldn't even consider having propane in either my house or van for what it's worth (which isn't much)
I have natural gas at home and don't worry about it at all. I've had propane in RVs and didn't worry too much either. Inexpensive detection can prevent most serious problems.

Having said that I'd prefer an all-electric van camper if practical. Air conditioning and heat are still challenges due to amount of required energy.
 
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