Why We Ripped Out Our AGM Setup After Two Years (And Almost Didn’t)
Two in the morning, somewhere outside Joshua Tree, and our batteries were dead. Not low. Dead.
We had been running AGM batteries for motorhome power since we bought our rig in 2018, and we thought we knew what we were doing. Two 6-volt deep cycle batteries wired in series, a decent solar setup, careful about our usage. We never ran the microwave off battery. We turned off the water pump at night. We did everything right.
Except we did not account for the fact that AGM batteries only give you half their rated capacity before you start damaging the cells. Our 200 amp-hour bank was really a 100 amp-hour bank, and we had been slowly killing it for two years by draining it past 50 percent every few days. That night in the desert, the batteries gave up.
We spent the next morning researching lithium batteries, and the sticker shock almost sent us straight back to the auto parts store for another set of AGMs. Lithium cost three times as much. Maybe four times, depending on the brand. We could replace our dead AGMs for $400, or we could drop $1,500 on lithium and hope the internet hype was real.
What finally pushed us over the edge was not the capacity or the weight or the cycle life. It was the realization that we had already spent $400 on AGM batteries two years earlier, and now we were about to spend another $400, and in two more years we would probably be doing it again. Lithium batteries were not three times the price. They were three times the price once, versus AGM at full price every two years.
We ordered a set of lithium iron phosphate batteries from a brand we had never heard of, installed them in a Walmart parking lot using a YouTube video for guidance, and crossed our fingers.
The first week was unbelievable. We ran the air conditioner longer. We did not obsess over the battery monitor. We camped in the same spot outside Sedona where we had nervously rationed power with AGM, and this time we had juice left over at sunrise. It felt like cheating.
We thought we had solved the battery problem forever.
The Lithium Honeymoon Phase Wore Off—Here’s What Actually Happened
Everyone online says lithium is perfect. They are lying.
Three months after the install, we were boondocking in Colorado in October, and the temperature dropped to 28 degrees overnight. Our lithium batteries have a built-in battery management system that shuts off charging below 32 degrees to protect the cells. We woke up to a battery bank that would not accept a single watt from our solar panels, even though the sun was blazing and the panels were putting out full power. The batteries sat there, locked out, until the afternoon when the interior warmed up enough to let the BMS release.
We lost an entire morning of solar charging because of a safety feature we did not know existed.
Then there was the parallel wiring issue. We had wired two lithium batteries in parallel, which every forum said was fine, until we started getting weird voltage drops under heavy load. Turns out smart lithium batteries do not always play nice with each other when they are wired in parallel. The BMS systems can fight each other. Some brands have added extra programming to fix this, but ours had not, and we ended up rewiring the whole setup to isolate the batteries.
And yet, even with those problems, we would not go back to AGM. Lithium still gives us 90 percent usable capacity instead of 50. It still weighs half as much. It still charges faster and lasts longer. The honeymoon is over, but the marriage is solid.
When We Realized AGM Batteries Weren’t the Enemy
AGM gets unfairly trashed, and we are part of the problem.
If you are weekend camping in moderate climates and you have shore power most of the time, AGM is the smarter choice. It costs a quarter of what lithium costs, it handles cold weather better, and it does not require you to rewire your charging system or worry about BMS lockouts. We have friends who replaced their AGM batteries once in eight years and spent less total than we spent on lithium.
AGM also does not care if you forget to disconnect your solar panels during a freeze. Lithium will punish you for that mistake. AGM will keep working.
The real advantage of AGM is not performance. It is forgiveness. You can abuse an AGM battery and it will die slowly over two years. You can abuse a lithium battery and it will brick itself overnight and cost you $1,500 to replace.
Our Three Go-To Batteries for Motorhome Setups (And Why We Stopped Chasing the Perfect One)
We have tested enough batteries for motorhome power to know that there is no perfect answer, only trade-offs you can live with.
Our current setup is a 300 amp-hour lithium bank made from two 12-volt batteries wired in parallel. We went with a mid-tier brand after our first set of cheap lithium batteries started showing voltage sag after 18 months. The upgrade cost us $1,800, but the batteries have been rock solid for two years now. We get three days of boondocking in summer with the air conditioner running at night, and the batteries recharge fully by noon the next day with our 600 watts of solar. The weight savings alone—about 200 pounds compared to the equivalent AGM setup—made a noticeable difference in how our rig handles.
The failure mode we did encounter was our own fault. We left the rig parked in Florida for two months in July and August with the batteries fully charged and the solar panels connected. Lithium batteries do not like sitting at 100 percent in high heat. When we came back, one of the batteries had a swollen case and the BMS had shut it down permanently. We learned that lesson for $900.
For our AGM recommendation, we keep coming back to Interstate. We used a pair of Interstate 6-volt deep cycle batteries in our old setup, and they lasted two and a half years of hard use before they started losing capacity. They cost $380 for the pair, they were available at any auto parts store, and they never surprised us with weird behavior. You get what you pay for with batteries, and Interstate delivers exactly what it promises.
The AGM brands we avoid are the ones that all come from the same manufacturer but cost different prices. Crown, Lifeline, and Trojan are all made by East Penn, which means you are paying for a label, not a better battery. We would rather buy Interstate and know exactly what we are getting.
We also tested Renogy lithium batteries for six months and found them overpriced for what you get, Battle Born batteries that cost more than our solar panels, a set of cheap Amazon lithium batteries that died in 14 months, and one AGM battery from a truck stop that we do not even remember the name of because it was garbage.
The Battery Mistakes That Cost Us Money (And How to Avoid Them)
Our biggest mistake was undersizing our first lithium battery bank. We calculated our amp-hour needs based on our AGM usage, which made no sense because the whole point of lithium was to use more power. We bought a 200 amp-hour lithium setup to replace our 200 amp-hour AGM setup, and then we immediately started running the air conditioner twice as long and draining the batteries every night. Six months later we were shopping for more batteries because we had not actually solved the problem, we had moved it.
The second mistake was not understanding our climate. We camp in the desert in winter and in the mountains in summer, which means our batteries see both extremes. Lithium does not like cold, and it really does not like heat. Our first set of batteries lived in an uninsulated battery compartment that hit 140 degrees in the Arizona sun, and they degraded faster than they should have. We added reflective insulation material and a small ventilation fan, and our second set has lasted twice as long. AGM batteries would have handled the heat better, but we wanted the capacity, so we had to engineer around the weakness.
The third mistake was trusting our RV’s factory charging system to handle lithium. It did not. The converter was designed for lead-acid batteries and kept trying to push 14.8 volts into our lithium bank, which the BMS did not appreciate. We had to install a new lithium-compatible charger, which added another $400 to the total cost of the upgrade. If we had known that upfront, we might have stuck with AGM for another year and saved up for the full system replacement.
We are still not sure we have the charging profile dialed in perfectly. Every few months we notice something weird—voltage spikes, uneven cell balancing, one battery charging faster than the other—and we tweak the settings again. AGM never required this much attention.
Figure Out Your Real Battery Needs Before You Buy Anything
We spent $1,800 on lithium batteries we did not need because we asked the wrong questions.
The question we asked was: what is the best battery? The question we should have asked was: how many amp-hours do we actually use in a day, and how many days do we need to go between charges?
We finally sat down and tracked our power usage for a week. We wrote down every time we ran the water pump, the furnace, the lights, the TV, the air conditioner. We added it all up and realized we were using about 80 amp-hours per day in moderate weather, and closer to 150 amp-hours per day when we were running climate control. That meant a 300 amp-hour lithium bank gave us two days of autonomy, or a 400 amp-hour AGM bank gave us one day. Once we knew those numbers, the decision got a lot simpler.
Climate matters more than we thought. We camp in places where the temperature swings from 130 degrees during the day to 50 at night, and that kind of cycle eats batteries alive. Cheap batteries go from flexible to crumbly in under two years. Even good batteries degrade faster in extreme heat and cold. If you are parking your rig in Florida for the summer or Minnesota for the winter, your battery lifespan is going to be shorter than someone who lives in California year-round, and you need to budget for that.
Your tolerance for maintenance also matters. Lithium requires you to pay attention. You need to monitor your BMS, adjust your charging profile, insulate your battery compartment, and disconnect your solar in freezing weather. AGM works. If you do not want to think about your house batteries more than once a year, AGM is the right answer even if lithium has better specs.
Before you read another review or watch another YouTube video, go camp for a week and write down your actual amp-hour usage. Check your battery monitor every morning and every night. Track how much solar you collect and how much you use. Most people overestimate their needs by 50 percent, and then they buy twice as much battery as they need and complain about the cost.
We did exactly that, and we are still paying for it.
What We Would Do Differently If We Started Over
If we were buying batteries for motorhome power today, we would start with AGM and upgrade to lithium only after we had proven we needed the extra capacity.
That is the opposite of what we actually did, and it is the opposite of what every RV forum will tell you to do, but it is the truth. AGM is cheaper, simpler, and more forgiving. Lithium is better in almost every measurable way, but it costs more and punishes mistakes harder. The smart move is to learn on AGM, figure out your real power needs, and then upgrade to lithium when you have outgrown what AGM can deliver.
We would also budget for the entire system upgrade, not the batteries for motorhome installations. Lithium needs a lithium-compatible charger, a better battery monitor, possibly a pure sine wave inverter, and definitely better insulation in the battery compartment. The batteries themselves are only half the cost. The other half is all the stuff you need to make them work right.
And we would test our batteries at an auto parts store twice a year. Most chain stores will test your battery bank for free and tell you how much capacity you have lost. We did not know that was an option until we had already killed two sets of AGM batteries by running them too low. If we had tested them after the first year, we would have known they were degrading and we could have adjusted our usage before they died completely.
We also wish we had found more boondocking tips and resources earlier in our journey, because proper power management makes all the difference when you are camping off-grid for extended periods.
We still think lithium is the right choice for serious boondocking, but we also think most people do not need serious boondocking batteries. They need something reliable that will get them through a weekend without shore power, and AGM does that for a quarter of the price. If you are not sure which batteries for motorhome use you need, you probably need AGM.
That night outside Joshua Tree, when our batteries for motorhome power died at two in the morning, we thought we had learned the lesson. Turns out we had only learned half of it. The other half took two more years, another $2,000 in mistakes, and a complete rethinking of how we approached batteries for motorhome living.
