Battery types refer to the distinct electrochemical cell chemistries—primarily Lead-Acid (Flooded, AGM, Gel) and Lithium Iron Phosphate (LiFePO4)—that dictate a storage bank's voltage curve, depth of discharge limits, and physical footprint. The chemistry you choose fundamentally changes your charge controller configuration, required BMS (Battery Management System) presence, wire sizing for peak inverter draws, and the physical ventilation requirements of your battery enclosure.
The Core Battery Types in Modern DC Systems
When building a 12V, 24V, or 48V power system, you are realistically choosing between three main chemistries. While NMC lithium exists, its thermal runaway risk and steep voltage drop make it unsuitable for most DIY solar or camper builds.
| Chemistry | Nominal Voltage (4S/6S) | Usable Depth of Discharge (DoD) | Cycle Life (to 80% health) | Cost per Usable kWh (Approx) |
|---|---|---|---|---|
| Flooded Lead-Acid (FLA) | 12.0V (6S) | 50% | 500 - 800 | $250 - $350 |
| AGM / Gel (Sealed Lead-Acid) | 12.0V (6S) | 50% | 400 - 600 | $350 - $450 |
| LiFePO4 (Lithium Iron Phosphate) | 12.8V (4S) | 80% - 100% | 3,000 - 5,000+ | $150 - $250 |
Crucial takeaway: A 100Ah FLA battery yields ~600Wh of usable energy, while a 100Ah LiFePO4 battery yields ~1,280Wh of usable energy. When comparing prices, you must divide the lead-acid sticker price by half to compare it fairly against lithium.
What Chemistry Changes in Your Installation
Swapping battery types is not a simple drop-in replacement; it alters the electrical behavior of the entire DC bus.
- Charge Profiles: FLA requires a high-voltage absorption phase (14.4V - 14.8V) to mix the electrolyte and prevent stratification, followed by a float phase (13.5V). LiFePO4 requires a strict constant current/constant voltage (CC/CV) profile, typically absorbing at 14.2V to 14.4V, and requires zero float voltage. Applying a continuous 13.5V float to lithium will degrade the cells and confuse the BMS.
- Voltage Sag and Wire Sizing: Lead-acid batteries suffer from severe voltage sag under heavy loads due to internal resistance (Peukert's Law). A 12V FLA battery might sag to 11.2V when pulling 150A, potentially tripping your inverter's Low Voltage Disconnect (LVD). LiFePO4 maintains a rigid ~13.2V under the same load until it is nearly empty. This means you can sometimes use slightly smaller busbars with lithium, though you must still size wires for the maximum continuous ampacity of the inverter.
- Ventilation and Enclosures: FLA batteries off-gas hydrogen and oxygen during the absorption charge phase. They must be installed in ventilated enclosures, never in a sealed bedroom or unvented camper cabinet. LiFePO4 cells do not off-gas during normal operation and can be installed in sealed, indoor compartments.
Worked Example: Sizing a 2000W Inverter Bank
Let's look at a real-world scenario to see how battery types change your physical build. You need to power a 2000W 12V inverter running a microwave and coffee maker for 2 hours at an average 50% load (1000W continuous draw).
The Lead-Acid Path:
To get 2000Wh of usable energy at a 50% DoD limit, you need a bank with 4000Wh of total capacity. At 12V nominal, that requires 333Ah of rated capacity. You might buy four 6V 220Ah FLA golf cart batteries (wired in a 2S2P configuration). This gives you 264Ah at 12V (3,168Wh total). Usable capacity is only 1,584Wh. Furthermore, when the microwave kicks on (surge to 1800W), the inverter pulls ~170A. The FLA bank's voltage will sag heavily, likely dropping below 11.5V and tripping the inverter's low-voltage alarm mid-cook.
The LiFePO4 Path:
To get 2000Wh of usable energy at an 80% DoD, you need 2500Wh of total capacity. A single 12.8V 200Ah LiFePO4 battery provides 2,560Wh total, yielding 2,048Wh usable. When the microwave surges to 1800W (pulling ~170A), the internal resistance of the LiFePO4 cells is so low that the terminal voltage barely drops below 12.8V. The inverter runs perfectly, and you saved 60 lbs of weight and half the physical footprint.
Where You Meet Battery Types in Practice
You will encounter the practical differences between battery types in three specific configuration menus on your bench:
- MPPT Charge Controller Settings: On a Victron SmartSolar MPPT, selecting the 'LiFePO4' preset disables the automatic temperature compensation and float stages that are mandatory for lead-acid. If you leave a lithium bank on the 'AGM' preset, the controller will attempt to equalize or float the cells, eventually triggering the BMS over-voltage protection and shutting down your solar array.
- Inverter Low Voltage Cutoff (LVC): For FLA, you typically set the LVC to 11.5V to protect the battery from deep discharge. For LiFePO4, you set the inverter LVC to 12.0V or 12.5V. Why? Because a LiFePO4 cell drops off a cliff below 12.0V; if you wait for 11.5V, the BMS will hard-disconnect before the inverter can gracefully shut down, causing a DC voltage spike that can blow inverter MOSFETs.
- Battery Monitor Shunt Configuration: When setting up a Victron BMV-712 or Renogy 500A shunt, you must input the correct Peukert exponent. Use 1.25 for FLA/AGM, and 1.05 for LiFePO4. If you use 1.25 on lithium, the monitor will artificially under-report your remaining capacity during high-current draws.
Decision Tree: Which Battery Type to Buy
Use this decision matrix to select the correct chemistry for your specific application. Do not overcomplicate this; for 95% of modern off-grid and mobile builds, lithium is the only logical choice.
| Your Scenario & Constraints | Recommended Chemistry | Concrete Pick & Value |
|---|---|---|
| Weekend cabin, backup UPS, budget strictly under $150, infrequent cycling (once a month) | AGM (Sealed Lead-Acid) | Pick: Weize 12V 100Ah AGM (~$130) |
| Golf cart, forklift, or extreme high-temperature ambient environments (>110°F / 43°C) where BMS thermal cutoffs are a nuisance | Flooded Lead-Acid (FLA) | Pick: Trojan T-105 RE 6V 250Ah (Buy local to avoid hazmat shipping) |
| Daily cycling, solar off-grid, camper van, high inverter loads, limited physical space, or marine house bank | LiFePO4 (Lithium Iron Phosphate) | Default Pick: LiTime 12V 100Ah LiFePO4 (~$250) |
Common Confusions and FAQ
Can I mix LiFePO4 and Lead-Acid in the same bank?
No. Their resting voltages and charge acceptance curves are completely different. The lead-acid battery will perpetually undercharge and sulfate, while the lithium battery will be pushed into over-voltage by the absorption phase required by the lead-acid. Keep chemistries on entirely separate DC buses with separate charge controllers.
Do I need to wire a BMS for LiFePO4?
For DIY cylindrical cell builds (like building a 280Ah bank from raw EVE or Lishen prismatic cells), yes, you must wire an external BMS like a Daly or JK BMS to balance the cells and provide over-current protection. However, if you buy a drop-in 12V LiFePO4 battery (like the LiTime or SOK mentioned above), the BMS is already integrated inside the steel or ABS case, wired directly to the main terminals.
Why do people say lithium is bad for cold weather?
LiFePO4 batteries discharge perfectly fine in sub-zero temperatures. The danger is charging them below 32°F (0°C). Charging lithium below freezing causes lithium plating on the anode, permanently degrading the cell and creating internal short-circuit risks. Quality drop-in batteries include a 'Low Temperature Charge Protection' feature in the BMS that physically blocks incoming charge current if the internal thermistors read below freezing. If you build your own raw-cell bank, you must manually disable your solar charge controller or add a battery heating pad.
For further reading on DC system integration and charge profiles, refer to the Victron Energy Lithium Basics Guide and the Department of Energy's Solar Plus Storage documentation. Always verify your specific inverter's manual for exact LVD and charge profile parameters before commissioning your bank.
