The sticker price is lying to you
You’ve probably seen the number already. A 100Ah AGM battery runs around $209 as of 2026, and a 100Ah lithium battery from a name-brand maker can run $625 to $925. On paper that looks like lithium costs three to four times more. You’ll want to fuse this next thought before you go any further: the sticker price is not the cost of the battery. It’s the cost of one battery. What you actually pay over a 10-year van build is the sticker price divided by how much usable energy you get out of it before it’s junk. That’s cost per amp-hour, and it flips the comparison almost every time.
I’ve wired both chemistries into vans, and I’ve replaced AGM banks for clients who bought “cheap” the first time and paid twice. Here’s the math I actually use when someone asks me which battery to buy.
Upfront pricing, as of 2026
Prices move constantly on solar gear, so treat every number below as approximate and check current pricing before you order. Here’s what a 100Ah 12V battery costs right now in each category.
| Battery | Chemistry | Price (approx, 2026) | Rated cycle life | Usable capacity (recommended DOD) |
|---|---|---|---|---|
| Renogy Deep Cycle AGM 100Ah | AGM lead-acid | around $209 | ~300-500 cycles at 50% DOD | 50Ah |
| Budget LiFePO4 (Ampere Time / Redodo style, 100Ah) | LiFePO4 | around $280-$320 | ~2,000-3,000 cycles (commodity BMS) | 100Ah |
| Renogy Pro Series 100Ah LiFePO4 | LiFePO4 | around $630 | ~3,000+ cycles | 100Ah |
| Battle Born 100Ah LiFePO4 | LiFePO4 | around $925 | 3,000-5,000 cycles | 100Ah |
You’ll notice AGM only gives you half its rated capacity as usable power. That’s not marketing spin, it’s chemistry. Pull an AGM battery below 50% state of charge on a regular basis and you’re grinding down its plates every single cycle. Lithium doesn’t have that problem. A quality LiFePO4 cell can be routinely discharged to 0-10% without the same damage, which is why the spec sheet says “100% usable” and means it.
The real equation: cost per usable amp-hour cycle
Here’s the formula I use to cut through the sticker price noise. It’s not complicated, but almost nobody runs it before buying.
Cost per Ah-cycle = Battery Price / (Usable Ah x Rated Cycle Life)
Let’s plug in real numbers using the prices above.
AGM (Renogy 100Ah, ~$209):
Usable capacity = 100Ah x 50% DOD = 50Ah Cycle life (conservative, deep-cycle service) = 500 cycles Cost per Ah-cycle = $209 / (50 x 500) = $209 / 25,000 = $0.00836 per Ah-cycle
Battle Born LiFePO4 (100Ah, ~$925):
Usable capacity = 100Ah x 100% DOD = 100Ah Cycle life (conservative floor of the 3,000-5,000 range) = 3,000 cycles Cost per Ah-cycle = $925 / (100 x 3,000) = $925 / 300,000 = $0.00308 per Ah-cycle
Run the numbers and the AGM battery is actually costing you almost three times more per usable amp-hour than the “expensive” lithium, even using the low end of Battle Born’s cycle rating and the low end of a realistic AGM lifespan. This is the biggest cost swing in the whole build, and it’s the opposite of what the price tags suggest.
Even a budget LiFePO4 pack in the $300 range beats AGM on this math, since you’re getting double the usable capacity per rated Ah and roughly 4-6x the cycle count. The catch, and it’s a real one, is that commodity BMS boards in budget packs have shown inconsistent low-temperature cutoff behavior in cold-weather testing. That’s a safety and reliability tradeoff, not just a price one. If your van sees regular freezing nights, that’s worth paying for the better BMS.
Plug your own daily amp-hour draw into the freeOff-Grid Van Electrical Calculator on the homepage and you can run this same equation against your actual usage pattern instead of a generic 100Ah example. Full-timers who cycle a battery almost every day of the year will see the lithium payoff even faster than weekend users will.
Depth of discharge is the hidden tax on AGM
Here’s where most people get this wrong when they’re sizing a bank on a budget. If you need 100Ah of usable capacity per day and you’re going AGM, you don’t buy one 100Ah AGM battery. You need to buy 200Ah of rated AGM capacity, because you can only safely pull half of it. That means two Group 27 AGM batteries at roughly $209 each, or about $418, just to match what one 100Ah lithium battery gives you in usable power.
That doubles your weight too. Two 100Ah AGM batteries run somewhere around 130-140 lbs combined. A single 100Ah lithium battery like the Battle Born comes in at 31 lbs. In a van build where every pound matters for payload and fuel economy, that’s not a small detail. If you want to calculate your exact load and weight distribution before buying, check out our OffGridVanCalc Homepage to map out your entire system.
Wiring and fusing: the differences that actually matter
Chemistry changes your wire sizing math too, because it changes how much current your bank can actually deliver and accept.
Say you’re running a 2,000W inverter off a 12V bank. At full load that’s roughly 166A continuous on the DC side (2000W / 12V), and real-world draw with inverter inefficiency pushes it higher, closer to 180A. That’s 2/0 AWG copper territory for anything under about 10 feet of total cable run, not the 4 AWG a lot of people default to because it’s what’s in stock at the auto parts store. Undersized cable under sustained load heats up, and heat is where fires start.
- Fuse placement: Your main battery fuse needs to sit within 7 inches of the battery’s positive terminal, on the wire, before it reaches anything else in the system. Not at the busbar. Not at the inverter. At the battery.
- Fuse sizing (lithium): Size it to protect the wire, not the battery. Battle Born rates the 100Ah at 100A continuous and 200A surge for 30 seconds, so a 150-200A ANL or MEGA fuse on properly sized cable is typical, depending on your specific wire gauge’s ampacity rating.
- Fuse sizing (AGM): AGM banks can usually deliver higher instantaneous surge current than lithium of the same rated Ah, which sounds like a benefit until you realize it also means a dead short releases more energy, faster. Don’t undersize the fuse just because the battery “feels safer.”
Safety differences you shouldn’t gloss over
AGM batteries are sealed, but they’re not immune to venting. Overcharge one, or charge it in a poorly ventilated compartment with a failing charge controller, and it can vent hydrogen gas. It’s a sealed lead-acid design specifically to minimize this, but “minimize” isn’t “eliminate,” and it’s why you never mount an AGM bank in a fully sealed compartment with zero airflow.
Lithium’s failure mode is different. A quality LiFePO4 battery has a built-in BMS that cuts charging below freezing to prevent lithium plating on the anode, which is the actual danger point for this chemistry. ou can read more about the detailed safety metrics of Lithium Iron Phosphate battery chemistry on Wikipedia. Cheap BMS boards have shown inconsistent cutoff behavior in cold-weather testing, meaning some budget packs either cut off too aggressively (leaving you without power on a cold night) or not aggressively enough (risking cell damage). If you’re building for genuine four-season use, this is where the extra couple hundred dollars for a name-brand BMS earns its keep.
The 10-year total cost picture
Assuming daily cycling over a decade of full-time van life, roughly 3,650 cycles, here’s how the real replacement math shakes out per 100Ah of usable capacity.
| Setup | Units needed for 100Ah usable | Approx. replacements over 10 years | Approx. 10-year total cost |
|---|---|---|---|
| AGM (2x 100Ah for 100Ah usable) | 2 batteries | ~6-7 full bank replacements | $2,900-$3,300+ |
| Budget LiFePO4 (1x 100Ah) | 1 battery | 1-2 replacements (BMS-dependent) | $300-$960 |
| Battle Born 100Ah LiFePO4 | 1 battery | 0-1 replacements (within warranty) | $925-$1,850 |
These are directional numbers, not a guarantee, since actual cycle life depends on temperature, charge rate, and how deep you actually discharge each cycle. But the pattern holds across every credible source I checked: AGM’s low DOD ceiling and shorter cycle life make it the more expensive option over any build longer than a couple of years, even though it wins on day-one price.
Which one actually makes sense for your build
- Weekend or occasional use, tight budget: AGM can still make sense here. If you’re cycling the bank 20-30 times a year instead of 300+, you may never hit the point where lithium’s cycle-life advantage pays off before you sell the van.
- Full-time or frequent use: Lithium wins on cost per Ah within 1-2 years of daily use, plus you get half the weight and no 50% DOD ceiling to work around when sizing your solar and inverter.
- Cold-climate builds: Spend the extra money on a name-brand BMS. This is not the place to save $300 on a budget pack.
- Tight weight budget (4×4 vans, weak alternators): Lithium’s weight and higher charge acceptance both work in your favor here.
FAQ
Can I mix AGM and lithium in the same bank?
No. Different chemistries have different charge voltage curves and internal resistance, and mixing them in parallel leads to uneven charging and premature failure of one or both.
Do I need a different charge controller for lithium vs AGM?
You need a controller with a lithium (or “user” / custom) charge profile available. Running a lithium-specific bulk and absorption voltage curve through an AGM-only controller will undercharge or overcharge your lithium bank over time.
Will lithium actually last the full 10 years?
A name-brand 100Ah LiFePO4 battery cycled once a day sits right around the edge of its 3,000-5,000 cycle rating over a decade, and most makers back that with a 10-year warranty, which tells you they’ve done this math too.
Reality check
Run these numbers against your own daily amp-hour draw before you order anything, since your actual usage pattern changes the payback timeline more than any spec sheet will. And regardless of which chemistry you land on, have your final wire gauge, fuse sizing, and charge controller settings checked by a qualified 12V installer before you flip the main switch. The math above gets you close. It doesn’t replace a second set of eyes on a live battery bank.