AGM Battery inside where we sleep?

[S. Heisley]

I have had the same AGM battery, a "wheelchair" battery inside my cabin for 10 years. While I did vent mine to the outside wall, according to the battery company, I didn't have to. They do outgas a tad and I simply felt better adding the vent. People in wheelchairs set them right next to their bed at night and charge them, but the room that they are in is most likely a little bigger than our teardrops and tiny trailers. Also, our trailers, especially well-done homemade ones, tend to be air-tight. House and apartments? Not so much.

My 10 YO battery finally died last fall but I will be buying another AGM shortly. I really like them. The one I bought before is no longer available so I will most likely go with a Northstar. (Northstars have been known to go 12 years. We'll see....)

If you decide to put in a vent, simply put some RV putty or Butyl tape around/under the rim of the vent. It should be fine that way.

[friz]

I didn't want to sacrifice the space. So I put it underneath.

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[GuitarPhotog]

My 60AH AGM battery has been inside the cabin, next to my pillow, for 10 years now with no problems. I often camp with a hookup and so the battery may be charging at any time. According to the manufacturer, an AGM battery vents hydrogen only to prevent explosion due to overcharging. So the solution is to ensure that you are never overcharging. That's best done with a smart charger/converter like the PD40405 that I installed in my teardrop, at the same time as the battery!

<Chas>

[Tom&Shelly]

My 60AH AGM battery has been inside the cabin, next to my pillow, for 10 years now with no problems. I often camp with a hookup and so the battery may be charging at any time. According to the manufacturer, an AGM battery vents hydrogen only to prevent explosion due to overcharging. So the solution is to ensure that you are never overcharging. That's best done with a smart charger/converter like the PD40405 that I installed in my teardrop, at the same time as the battery!

<Chas>

Works great while everything is working. What happens if one cell in your AGM battery goes bad before the rest? Then your "smart" charger tries charging a 10.5 volt battery to 12 volt levels.

Your design depends on all of the relatively inexpensive parts working correctly through out the lifetime of your camper. You bet your life!

In fact, hydrogen molecules are so small, I suspect they'll dissipate in a teardrop cabin so fast you'll be fine even then. Maybe...

Tom

[S. Heisley]

My 60AH AGM battery has been inside the cabin, next to my pillow, for 10 years now with no problems. I often camp with a hookup and so the battery may be charging at any time. According to the manufacturer, an AGM battery vents hydrogen only to prevent explosion due to overcharging. So the solution is to ensure that you are never overcharging. That's best done with a smart charger/converter like the PD40405 that I installed in my teardrop, at the same time as the battery!

<Chas>

Works great while everything is working. What happens if one cell in your AGM battery goes bad before the rest? Then your "smart" charger tries charging a 10.5 volt battery to 12 volt levels.

Your design depends on all of the relatively inexpensive parts working correctly through out the lifetime of your camper. You bet your life!

In fact, hydrogen molecules are so small, I suspect they'll dissipate in a teardrop cabin so fast you'll be fine even then. Maybe...
Tom

Two questions/thoughts:

Chas, what brand AGM battery did you purchase?

Tom, at 10.5, the battery is considered dead and needs replacing. But you probably know that. A battery should be checked before the start of charging and not allowed to get below 11.6. If that check reads 10.6 or below, it does little to even try to charge it. However, out of curiosity, I tried it and there was no out-gassing, even after a couple hours, and the battery did not get too hot. It would make sense that there's a safety mechanism built in to the controller since the charger seems to "know" when the battery is fully charged and changes its charging to a maintenance routine or whatever, but my knowledge in that area is slim. Also, From my experience, the battery only seems to discharge fumes when I first begin the charging. I don't know what that's about but it might be a good thing in your case.

From what I've read, Lithium-ion batteries last an average of 3 to 5 years. AGM batteries can last up to 12 years. (You're on borrowed time, Chas.) As well as their longevity, AGMs have another advantage. You can fully charge them in the fall (say, October?) and they will hold that charge until you pull the trailer out of its hidey-hole in April, provided they have no "draws", are disconnected.

[Tom&Shelly]

[Tom, at 10.5, the battery is considered dead and needs replacing. But you probably know that. A battery should be checked before the start of charging and not allowed to get below 11.6. If that check reads 10.6 or below, it does little to even try to charge it. However, out of curiosity, I tried it and there was no out-gassing, even after a couple hours, and the battery did not get too hot.

Well, two points here: 1. It may not have done it that time, but it might another, 2. How do you know there was no out-gassing? Without a hydrogen detector, I don't think one could tell. Its not clear to me that hydrogen molecules, being as small as they are and at a relatively low but positive pressure, would even make some sort of out-gassing noise like air. If in a ventilated area (which I hope you were in when you tried it), the hydrogen molecules would likely have diffused so quickly even a good detector wouldn't find any. (Exactly why the AGM battery manufacturers say they should be in vented battery compartments, or out in the air.)

Oh, and suppose a cell fails while the battery is charging?

It would make sense that there's a safety mechanism built in to the controller since the charger seems to "know" when the battery is fully charged and changes its charging to a maintenance routine or whatever, but my knowledge in that area is slim.

I don't know either. Neither the charger in my PD 4045 nor the one in my solar controller mention anything like a low voltage check. I did read something on the inter-webs about AGM batteries being able to drop below 10.5 volts (all cells down an equal amount, rather than one bad one) and still being good enough to "revive", whatever that may mean, so these chargers may, in fact, not look at low voltages. The PD 4045 still powers the DC systems in the teardrop when there is no battery (0 volts), so I suspect it may have voltage to offer anything across the battery terminals. (I'll put a meter on it in the next week or so when I have the system back together.)

Also, From my experience, the battery only seems to discharge fumes when I first begin the charging.

Sharon, that is really concerning. Hydrogen has no odor, and you certainly won't see it. Are you smelling/seeing hydrogen-sulfide, or something else that is poisonous? I don't know. It shouldn't be discharging any fumes.

My basic point is that it probably isn't a good idea to assume an AGM battery or smart charger is always going to work as specified. There is a reason all of the AGM battery manufacturers say they must be in vented battery compartments, and I don't think it's just to appease the lawyers. We're talking about rare events, but ones with potentially life threatening consequences. I do know that when they build systems that do similar things in manned aircraft, spacecraft, or submersibles, a lot more money goes into ensuring a design safe for that environment.

But as the announcer at Woodstock said "hey, it's your trip." (Of course, it may also be your family's trip.)

Tom

[S. Heisley]

Hi, Tom:

When my charger starts up, the fan runs for maybe 20 seconds and that's when I smell the odor. It's possible that the charger is clearing any residue from the air of the compartment before starting to charge the battery. I don't know the reason but I do remember reading that the fan will run for a short period at start-up.

As far as having the AGM battery in a ventilated box, yes, even wheelchairs are like that. But, since the wheelchair sits right next to the person while they sleep, I don't think the fumes are the concern. Rather, I suspect that the ventilation is to prevent possible explosions that might occur from build-up within a small, unventilated box. However, your questions and concerns might be best answered by a manufacturer or a company that regularly handles all types of batteries.

Best Wishes

[Tom&Shelly]

Hi, Tom:

When my charger starts up, the fan runs for maybe 20 seconds and that's when I smell the odor. It's possible that the charger is clearing any residue from the air of the compartment before starting to charge the battery. I don't know the reason but I do remember reading that the fan will run for a short period at start-up.

Yes, that's probably where the smell is coming from, not the battery.

As far as having the AGM battery in a ventilated box, yes, even wheelchairs are like that. But, since the wheelchair sits right next to the person while they sleep, I don't think the fumes are the concern. Rather, I suspect that the ventilation is to prevent possible explosions that might occur from build-up within a small, unventilated box. However, your questions and concerns might be best answered by a manufacturer or a company that regularly handles all types of batteries.

Best Wishes

Yes, it would be difficult to imagine suffocating from hydrogen. I'm not sure that it would even be possible, since the molecules are so much smaller than oxygen, carbon dioxide, etc. that they don't really displace the larger molecules when mixed in the air.

It's the build up, and explosion danger that I'm sure the battery manufactures are concerned with. As I said above, even in a space as small as a teardrop, it's hard to imagine the hydrogen building up without finding a way to escape, but, since the failure would be catastrophic, it's worth the simple expedient of including a proper vent. A normal room, where a wheel chair owner would likely sleep, I'd guess would be safe enough. Since the hydrogen molecules are so much smaller, they are also lighter than the main molecules in air, so when they bump into each other, the hydrogen molecules go that much faster, and diffuse through the air pretty quickly. Also because they are lighter, they tend to rise. (Most of my knowledge of hydrogen comes from crewing and flying in a hydrogen balloon, btw.)

FWIW, in my teardrop (still under construction) the battery is to the rear of the axle, under the floor in the galley. Around the battery box is about a 1/8 inch gap between that and the floor, which I believe is plenty of ventilation for hydrogen. (And, btw, meets the requirements someone posted above, iirc.)

Anyway, my totally inexpert advice for anyone considering putting an AGM battery in the cabin is to make sure there is a good vent for any hydrogen gas in the unlikely event something goes wrong with the battery and charger. I would never assume they will always work as they are supposed to when there is a safety issue involved.

All the best.

Tom

[Tom&Shelly]

It would make sense that there's a safety mechanism built in to the controller since the charger seems to "know" when the battery is fully charged and changes its charging to a maintenance routine or whatever, but my knowledge in that area is slim.

I don't know either. Neither the charger in my PD 4045 nor the one in my solar controller mention anything like a low voltage check. I did read something on the inter-webs about AGM batteries being able to drop below 10.5 volts (all cells down an equal amount, rather than one bad one) and still being good enough to "revive", whatever that may mean, so these chargers may, in fact, not look at low voltages. The PD 4045 still powers the DC systems in the teardrop when there is no battery (0 volts), so I suspect it may have voltage to offer anything across the battery terminals. (I'll put a meter on it in the next week or so when I have the system back together.)

Tom

Just to follow up on this. My PD 4045 puts out a charging voltage even when there is no battery connected. Since it doesn't shut off then, I don't think it shuts off when it detects a battery with low voltage (like a shorted cell).

Tom