Lead acid battery inside truck?

[98tcoma3rz]

Hey all,
Working on a dual battery setup. There is no room under my hood for a second battery. Can I mount a deep cycle, lead acid battery in my bed? It would be in a battery box but I would be sleeping back there with a cap on the truck. Worried about the gasses. Obviously they're a lot cheaper than AGM or sealed type batteries. I've read mixed opinions on this.

 

[thethePete]

If you seal the box and vent it with a rubber hose/tube to somewhere outside the truck bed, you'll be fine. Many OEMS use a similar design. Battery is in a sealed and vented compartment within the cabin. Still better to have an AGM, but off-gassing won't be an issue if you do it as I suggested.

 

[98tcoma3rz]

If you seal the box and vent it with a rubber hose/tube to somewhere outside the truck bed, you'll be fine. Many OEMS use a similar design. Battery is in a sealed and vented compartment within the cabin. Still better to have an AGM, but off-gassing won't be an issue if you do it as I suggested.

Ok cool. How big of a hose do you think? I see a lot of people use 6volt golf cart batteries? More amp hours?

 

[thethePete]

Can't help you with selecting a battery size, but if you look for a sealed box, it should have some type of vent already built into it. Most that I've seen are 1/4" line or so. It's not like there needs to be massive amounts of air movement.

 

[DaveInDenver]

Old air cooled VWs had their batteries under the back seats. Of course those weren't exactly well sealed compartments. Plus they tended to catch fire when an incorrectly sized battery would slip and arc on a seat spring and probably ignite the off gassing hydrogen, so maybe not the best model to study.

 

[waves]

Remember that batteries only gas when they are charging - they vent hydrogen from the negative during charging, and vent Oxygen from the positive - they consume hydrogen and don't gas when on discharge. So maybe sleeping in the cab when the battery is not charging is not a problem?

The sealed batteries have a vent on them - when the pressure reaches a point determined by the manufacturer the vent opens and burps gas. Some of the liquid wet cells don't have a vent. Main issue for these concerns is to be sure not to overcharge or not to charge at too high a voltage for the temperature that the battery is at. Overcharge will evaporate the H2O causing the specific gravity of the electrolyte to increase and you have to add water or a mixture of water and electrolyte to bring it back to normal.

Lower charging voltage for temperatures over 77F,/25C higher charging voltage for temperatures below 77F/25C. It depends on the specific Gravity of the battery electrolyte but generally the charging voltage is determined at 2.25 volts +/- 5mV per degree F per "cell" above or below 77F or 3mV per degree C above or below 25C per "cell". Batteries are constructed of multiples of 2 volt cells. A 12 volt has 6 cells, a 6 volt has 3 cells. This is the formula used to maximize battery life and to ensure the battery is charged to maximum capacity. A cold battery has less energy density than a warm battery. A hot battery is a very very bad thing.

6 volts have a higher energy density or capacity for the same footprint of a 12Volt, so you do get more amp-hours but need more space.

 

[dwh]

Yes, an Open Cell Flooded Lead-Acid will vent hydrogen and oxygen when charging. This does NOT mean it's safe to vent into the cabin - even if you aren't charging it while sleeping. The safety issue is hydrogen build-up in the cabin, which can be ignited by a spark or flame.

http://www.expeditionportal.com/forum/threads/65346-DIY-vented-battery-box-what-to-use



(And AGMs and GELs are also types of lead-acid batteries - just not open cell flooded lead-acid batteries.)

 

[waves]

Nah - Hydrogen is only combustible when it is between 4% and 74% of the room or cab volume. Since no truck cab is 100% airtight, hydrogen, the lightest element, will vent out of the cab with even the slightest opening. Do the calculations concerning how much hydrogen can be generated by a battery on overcharge or when charged with too high a voltage for the temperature and the SG of that battery, and you will find that it will take days to fill 4-74% of the volume of a cab with hydrogen, IF the cab is airtight.

Opening the cab and/or having a vent in the cab or a crack somewhere to the outside will insure that you never reach a combustible level and will be safe for sleeping in when not charging. Of course it also takes a source of ignition if you ever were to reach a combustible level.

I agree its not reccomended to have a battery in the cab, due to habit and an overabundance of caution which is not a bad thing, rather than science, but there's no reason to be too paranoid when a simple solution like not having an airtight cab and not being on charge when you sleep solves the problem. The thinking is much the same as how they make us turn off the cellphone transmitter on a plane. Cellphones CAN'T interfere with a modern commercial passenger jet plane's systems, but its based on tradition not science.

 

[98tcoma3rz]

Remember that batteries only gas when they are charging - they vent hydrogen from the negative during charging, and vent Oxygen from the positive - they consume hydrogen and don't gas when on discharge. So maybe sleeping in the cab when the battery is not charging is not a problem?

The sealed batteries have a vent on them - when the pressure reaches a point determined by the manufacturer the vent opens and burps gas. Some of the liquid wet cells don't have a vent. Main issue for these concerns is to be sure not to overcharge or not to charge at too high a voltage for the temperature that the battery is at. Overcharge will evaporate the H2O causing the specific gravity of the electrolyte to increase and you have to add water or a mixture of water and electrolyte to bring it back to normal.

Lower charging voltage for temperatures over 77F,/25C higher charging voltage for temperatures below 77F/25C. It depends on the specific Gravity of the battery electrolyte but generally the charging voltage is determined at 2.25 volts +/- 5mV per degree F per "cell" above or below 77F or 3mV per degree C above or below 25C per "cell". Batteries are constructed of multiples of 2 volt cells. A 12 volt has 6 cells, a 6 volt has 3 cells. This is the formula used to maximize battery life and to ensure the battery is charged to maximum capacity. A cold battery has less energy density than a warm battery. A hot battery is a very very bad thing.

6 volts have a higher energy density or capacity for the same footprint of a 12Volt, so you do get more amp-hours but need more space.

You are correct. I do not plan on sleeping in the cab while engine is running to charge the battery. I do, however plan on putting a solar panel on the roof to charge the battery. This is be a slow "trickle" charge though. Sounds like a sealed battery box with a vent is the best option. I don't need a ton of amp hours. They will be powering some lights, small air compressor, 2000 watt power inverter and some other small accessories. I think my best option would be (2) 6v batteries depending on the dimensions. Any recommended sizes? One larger 12 volt be better? I have a 130 amp alternator to help charge them (stock was 70amp, NOCO 200 amp battery isolator. Also I've read a few places about trying to stick with the same group size battery when running dual batteries. Does this apply when you have a battery isolator?

 

[dwh]

It doesn't have to fill the entire space, it just has to gather at a high point to become potentially exciting. It *won't* vent out of the slightest opening, unless that opening happens to be at the high point.


And then, there's always this - which requires neither overheat, overcharge nor filling up the available space with hydrogen at a high density:

 

[dwh]

Also I've read a few places about trying to stick with the same group size battery when running dual batteries. Does this apply when you have a battery isolator?

No, doesn't apply. Batteries have to be identical - age/size/type/manufacturer/etc. when tied into a permanent full-time bank. That way they age together rather than have one or another with lower resistance doing more work than the rest of the batteries in the bank.

When only tied during charging, it doesn't matter.

 

[dwh]

AND, any hydrogen which has gathered in a layer at a high point, is going to be at *what* density?

100%.

 

[waves]

"

You are correct. I do not plan on sleeping in the cab while engine is running to charge the battery. I do, however plan on putting a solar panel on the roof to charge the battery. This is be a slow "trickle" charge though. Sounds like a sealed battery box with a vent is the best option. I don't need a ton of amp hours. They will be powering some lights, small air compressor, 2000 watt power inverter and some other small accessories. I think my best option would be (2) 6v batteries depending on the dimensions. Any recommended sizes? One larger 12 volt be better? I have a 130 amp alternator to help charge them (stock was 70amp, NOCO 200 amp battery isolator. Also I've read a few places about trying to stick with the same group size battery when running dual batteries. Does this apply when you have a battery isolator?

Well, I'm not sure I understand your situation perfectly - but you're right, the size doesn't matter, I'd get as big as I could afford space for. If you are charging both batteries with the same charger, i.e. Alternator, meaning the same charging voltage, you should definitely keep with the same type (group) battery, meaning the same specific gravity,as your existing one. It really doesn't matter if you go with two 6 volts or one 12 volt, but if you have the space, I'd go with two 6 volts of the same group, due to increased energy density/capacity/amp-hours BUT make sure they are right next to each other and connected in parallel with oversized cables and connectors to prevent any charging voltage drop between the two. Leave 1-2 inch space between them, make sure that they can't be moved against each other while driving. You want space between them to ensure they have heat dissipation while on charge. Personally, I would definitely not use a sealed battery box. Just a box that has ventilation, an open top, and ventilation/not airtight cab. I use open space vent to the outside in the battery rooms I design or in some airtight situations and situations where theres too many batteries in too small of a space, I use active ventilation via redundant fans to ventilate, but you don't need to worry about that if your not airtight, especially if you're not overcharging with too high a voltage, and not too hot.

 

[waves]

AND, any hydrogen which has gathered in a layer at a high point, is going to be at *what* density?

100%.

Meaning it can't explode, right? H2 is only combustbile between 4-74% of volume.

 

[waves]

It doesn't have to fill the entire space, it just has to gather at a high point to become potentially exciting. It *won't* vent out of the slightest opening, unless that opening happens to be at the high point.


And then, there's always this - which requires neither overheat, overcharge nor filling up the available space with hydrogen at a high density:

Obviously it doesnt have to fill the entire space, it has to fill 4-74%. Do the calcs, see how long it takes to do that for a standard battery. As far as the video goes, looks like sensationlism to me, not science. Do you know what the health of that battery is? How old it is, meaning how close it was to shorting, or what the charger was set to, or how charged it already was before they put it on a charger, what the temperature was, etc, etc., and not many cabs have welder or metal grinder sparks being thrown.

Do something stupid like overcharging an already full battery in high temperature, or an old battery (>5-7 years depending on type) and guess what? Something stupid happens, so don't be stupid, thats all.

Hydrogen doesnt "gather" at a high point unless directed via a tube that way. Hydrogen disperses in all directions when not contained or directed to a specific spot. So have ventilation via several different solutions, understand that almost all cabs are not air tight anyway, don't be on charge when sleeping in the battery area, be smart.