There are three battery chemistries worth considering for an RV house bank: flooded lead-acid, absorbed glass mat (AGM, a sealed lead-acid type), and lithium iron phosphate (LiFePO4). We already covered lithium against AGM head-to-head. This guide adds flooded to the picture, because it is still the cheapest way to buy amp-hours, and explains when each one is the right answer rather than just the cheap or expensive one.
What the three actually are
Flooded lead-acid is the traditional deep-cycle battery: lead plates in liquid sulfuric acid, removable caps, and a need for periodic watering. Golf-cart 6 V batteries wired in series are the classic RV example.
AGM is lead-acid with the electrolyte held in fiberglass mats. Sealed, no watering, can be mounted on its side, and vents very little gas in normal use. Victron sells them as AGM Deep Cycle and Gel Deep Cycle ranges.
LiFePO4 is a lithium chemistry with a built-in battery management system (BMS). It is the safest lithium type for vehicles, tolerates deep discharge, and weighs far less. Examples: the Victron LiFePO4 Smart battery, the Victron Lithium SuperPack drop-in, and the Eco-Worthy 12 V 280 Ah.
Side by side
| Flooded | AGM | LiFePO4 | |
|---|---|---|---|
| Usable capacity (typical) | ~50% of rated | ~50–60% of rated | 80–100% of rated |
| Cycle life at that depth | roughly 300–500 | roughly 500–1,000 | 3,000+ |
| Weight, ~100 Ah 12 V | ~60–70 lb | ~60–70 lb | ~25–30 lb |
| Maintenance | Water, clean terminals, equalize | None | None |
| Mounting | Upright, vented box | Any orientation, sealed | Any orientation, sealed |
| Charging speed | Slow absorption tail | Faster than flooded | Fastest; accepts high current |
| Self-discharge in storage | Highest | Low | Very low |
| Cold-weather charging | OK, capacity drops | OK, capacity drops | Must not charge below freezing without protection |
| Voltage under load | Sags noticeably | Sags less | Nearly flat until empty |
| Up-front cost per rated Ah | Lowest | Middle | Highest |
| Cost per usable Ah over life | Highest | Middle | Lowest |
Cycle and weight figures are typical ranges, not a spec for any specific product. Check the datasheet for the battery you are buying.
Usable capacity is the number that matters
A "100 Ah" flooded or AGM battery is a 50 Ah battery in practice. Discharge lead-acid past half and its cycle life falls off quickly. A 100 Ah LiFePO4 gives you 80–100 Ah every cycle for thousands of cycles.
So to get 200 Ah of usable energy you need about 400 Ah of lead-acid (four large batteries, roughly 250 lb) or 200–250 Ah of lithium (one or two batteries, roughly 60 lb). On a Black Series HQ, where the battery box was sized for two lead-acid batteries, that difference decides whether you can go off-grid for a week or two nights.
Charging: each chemistry wants something different
- Flooded needs a bulk/absorption/float profile with a higher absorption voltage and periodic equalization. Most old RV converters were built for this.
- AGM needs a similar profile but a lower absorption voltage and no equalization. Overcharging AGM dries the mats and kills it.
- LiFePO4 needs a lithium profile: a fixed absorption voltage, short absorption, and low or no float. It also needs low-temperature charge cutoff.
That is why the charger matters as much as the battery. Every current Victron charger has selectable profiles for all three: the Blue Smart IP65 for shore power, the SmartSolar MPPT for solar, and the Orion-Tr Smart or Orion XS for alternator charging.
One more difference: lithium will pull whatever current the charger can deliver until nearly full. A tow vehicle alternator connected directly to a lithium bank can overheat. Use a DC-DC charger to limit that current; the Orion DC-DC guide explains why.
Cold weather
Lead-acid loses capacity in the cold but can be charged below freezing. LiFePO4 holds capacity better but must not be charged below about 32°F (0°C) or the cells plate with lithium and lose capacity permanently. Quality batteries include a low-temperature cutoff in the BMS; the Eco-Worthy 280 Ah lists low-temp protection, and Victron's Smart batteries report cell temperature to the charger via a BMS. If you winter camp, confirm the battery you buy has it.
Safety and mounting
Flooded batteries vent hydrogen while charging and must live in a vented compartment, upright. AGM and lithium are sealed and can go in an interior locker, which frees up the original battery box and shortens cable runs. Every chemistry needs a fuse close to the positive terminal; see fuses and circuit protection.
Which one should you buy?
Flooded: you are on a strict budget, the RV mostly sits on shore power, you can water the batteries, and weight is not an issue. It is a fine choice for a trailer that sees campgrounds and a few nights off-grid a year.
AGM: you want sealed, maintenance-free lead-acid, the RV came with an AGM-profile converter, or you camp in serious cold and do not want to manage lithium temperature limits. The Victron AGM Deep Cycle line runs $24.00–$546.00 by size.
LiFePO4: you boondock, run an inverter, care about weight, or plan to keep the RV more than a few years. The higher purchase price is spread over many more cycles, which is why cost per usable amp-hour ends up lowest. Pair it with a SmartShunt so you can see the flat voltage curve as a percentage rather than guessing.
Mixing chemistries
Do not parallel lithium with lead-acid on the same bus. They charge at different voltages and the lead-acid will either be overcharged or the lithium undercharged. If you keep a lead-acid start battery and a lithium house bank, separate them with a DC-DC charger, not a simple isolator.
Shop this
- Victron LiFePO4 Smart Battery 12.8V & 25.6V — from $444.00
- Eco-Worthy 12V 280Ah LiFePO4 (Bluetooth, low-temp protection) — $399.00
- Victron AGM Deep Cycle Battery — $24.00–$546.00
- Victron Blue Smart IP65 Charger 120V — from $52.50
- Lithium LiFePO4 Batteries (collection)