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Can AGM batteries run your Airstream all night long?

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All we can say is maybe.

Back in January, we stayed at a Harvest Host in Deming, New Mexico. The low that night was 19 degrees. We used our generator to keep our batteries fully charged for as long as possible, but eventually we turned it off and went to sleep. We got a rude awakening around 2:30 a.m. when our refrigerator sounded an alarm. Apparently the voltage coming from our batteries was too low to keep it happy. That sucked, but at least the furnace was still running. We turned the fridge off, knowing that our food would stay cold enough, and went back to bed. When morning arrived, we were relieved to find that the furnace still running, even though our batteries were severely depleted.

In early June, we stayed at another Harvest Host, this time in Portales, New Mexico. We arrived around six in the evening when it was at least 85 degrees, promptly blasted both fantastic fans, ran the water pump with reckless abandon, flushed the toilet liberally (water pump + macerator) and, of course, our refrigerator ran until we shut it off right before bed. (Lesson learned in January—lest you want a jolt at some ungodly hour, turn it off at night.) This time we didn’t have our generator with us, but we’d been driving all day in full sun which presumably would have kept our batteries completely charged. We went to sleep that night certain the fantastic fans would still be running in the morning. Nope. By 1:30 a.m., our batteries were so dead that the battery disconnect switch automatically engaged in order to rescue us from any further damage. (The timing of this was verified by Jill who woke up when the disconnect switch made its distinctive click-klack sound and the droning whir from our two fantastic fans was immediately replaced with a conspicuous silence.) From that point on, we couldn’t turn on the lights, flush the toilet, or run water until a few hours of morning sun began to replenish the batteries. Luckily, the sun rose much earlier than we did, so by the time I rolled out of bed, all I had to do was toggle the battery disconnect switch back on and like magic I was able to flush the toilet again. 🪄 đźš˝

In all likelihood, our battery capacity has been wrecked as a consequence of draining them too low on multiple occasions. That would explain why we managed to stay warm back in January, but were unable to stay cool in June. This quote from Battle Born Batteries supports this assessment:

If you are experiencing less than a night of use from your batteries, then you probably have damaged batteries. Lead acid batteries are significantly damaged anytime they are drained more than 50%. Most RVers drain them way deeper than this, and that is why they have such short lifespans. This is one of the major reasons many RVers choose to upgrade to lithium, as they are not damaged from deep discharges.

— Battle born batteries

I realize, of course, that Battle Born has a vested interest in selling lithium batteries to disillusioned lead-acid owners like us. Nevertheless, that statement accords well with information I’ve read elsewhere about lead-acid batteries. While it’s no secret that they suffer permanent damage when over-depleted, I never thought it would happen so quickly and to such a significant degree. I suppose the real answer to the question posed by this article is “probably when they’re new, but not in the long run.” Our AGM batteries have only been in use for about 16 months now but based on the fact that we cannot even run basic infrastructure—the fridge, water pump, fans, etc—for a single night on battery power, we’re planning on upgrading to lithium as soon as possible.

Making Your AGM Batteries Last

Later in June, we stayed at yet another Harvest Host location in Flagstaff, Arizona. With our recent dead battery experience still fresh in our minds, we approached this boondocking adventure very differently. As soon as we arrived, we put our fridge in night mode. In spite of the heat, we opened our fantastic fans but didn’t run them. Instead, we used this awesome battery powered fan by Geek Aire. We opened most of our windows and all four of our awnings. We ran the water pump as sparingly as possible. Instead of running the interior lights, we brought in our battery powered Devos Light Ranger inside. Just before bed, we turned the fridge completely off and ran both fantastic fans on low. When we woke up in the morning, the first thing I noticed was the sound of the fantastic fans still running. Our batteries weren’t dead. Mission accomplished!

Based on the stock battery voltage meter alone, it’s difficult to say exactly how much we saved with each of these precautions. For a more accurate assessment, we’d need something like this Victron SmartShunt installed. We’ll be getting one of those along with our lithium upgrade. For now, I’m operating on the unproven theory that our fridge is the main power goblin in our rig. I’m almost willing to say that if used our trailer like normal—water pump, toilet, lights—but kept the fridge off while we slept, our batteries could be stretched out for an entire night. Maybe we’ll give that a try next time we have the chance and see how it goes.

If we were able to magically rewind time back to the point when our batteries were new, there’s one thing I’d do differently to avoid over-depleting them. That is, make more use of the refrigerator’s ‘night mode’ when boondocking. We were told about this functionality when we took delivery, but promptly forgot all about it for nearly a year. And if that alone didn’t do the trick, we’d just completely turn the thing off while we slept. I really wonder if simply reducing the power consumption of that one appliance would have saved us from killing our batteries prematurely. Beyond that, we’re not sure what we could have done differently—other than never go without shore power, and that’s obviously not a viable solution.

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