Campervan Battery Guide: Sizing, Types & Installation (2025)

Choosing the right leisure battery is the single most consequential decision in your campervan electrical build. Everything else — solar panels, DC-DC charger, inverter — is sized around the battery. Get the battery wrong and you either run out of power at midnight or spend £400 more than you needed to.

This guide covers the complete picture: battery chemistry, sizing calculations with worked examples, UK product comparisons, wiring configurations, installation, monitoring, and maintenance. For how the battery fits into your overall electrical system, see our campervan electrical system guide.

Battery Chemistry: What You're Actually Buying

LiFePO4 (Lithium Iron Phosphate)

LiFePO4 is now the default choice for campervan builds. Unlike other lithium chemistries (NMC, NCA), LiFePO4 is inherently stable — it doesn't undergo thermal runaway the way phone or EV batteries can. This is why it's approved for use in enclosed spaces.

The chemistry works by moving lithium ions between an iron phosphate cathode and a graphite anode. The result is a very flat discharge curve: the battery holds close to 13.2V from about 90% state of charge (SoC) down to around 10% SoC, then drops steeply. In practice, this means your 12V appliances run at consistent voltage right until the battery is nearly empty — unlike AGM, which starts drooping in voltage as soon as discharge begins.

Key specifications:

The usable capacity difference is enormous in practice. A 200Ah AGM gives you 100Ah usable. A 100Ah LiFePO4 gives you 80–90Ah usable — similar storage at roughly similar cost, but half the weight and 10× the cycle life.

The 5-year cost comparison:

A 200Ah AGM at £180 lasts perhaps 400 cycles before capacity degrades significantly. If you're charging and discharging daily, that's about 18 months. Over 5 years you replace it 3–4 times: £540–£720 in batteries.

A 100Ah LiFePO4 at £250 lasts 3,000+ cycles. At daily use, that's 8+ years on one battery. Total 5-year cost: £250.

For any build that will see regular use, LiFePO4 is cheaper in the long run.

AGM (Absorbent Glass Mat)

AGM is a sealed lead-acid battery where the electrolyte is absorbed into fibreglass mats rather than flooding freely. This makes it spill-proof and maintenance-free, which is why it replaced flooded lead-acid for campervan use.

The main practical limitation is the 50% depth-of-discharge rule. Lead-acid chemistry suffers permanent capacity loss (sulphation) when cells are discharged below 50% SoC repeatedly. A 100Ah AGM has 50Ah of usable storage — and you must reliably charge it back to full frequently to prevent sulphation. Left at 50% SoC for weeks, it degrades.

AGM still makes sense for:

• Budget builds or weekend-only vans where the battery might be replaced after a few years anyway
• Vans where weight isn't a concern
• Systems where someone already owns AGM equipment and chargers
• Applications that don't require deep cycling

For anything that will see daily use — whether full-time van life or regular weekend trips — LiFePO4 is the better long-term choice.

Gel

Gel batteries use a silica-thickened electrolyte. They handle deep discharge slightly better than standard AGM and tolerate heat better, but they charge more slowly (maximum around 0.1C — a 100Ah gel can only accept 10A charge current, meaning a full charge takes 10+ hours). This makes them poorly suited to campervan use with fast alternator or solar charging.

Gel is increasingly rare in campervan applications and not something most builders should consider in 2026.

Understanding Battery Capacity: The Numbers That Matter

Battery capacity is rated in ampere-hours (Ah) — the current a battery can deliver over time. A 100Ah battery can theoretically deliver 1A for 100 hours, or 10A for 10 hours, or 100A for 1 hour.

However, capacity is affected by discharge rate (the Peukert effect) and temperature. Real-world usable Ah from the same battery will vary:

LiFePO4 is relatively immune to the Peukert effect compared to lead-acid. AGM suffers more significantly — a 100Ah AGM discharged at C/5 (20A) might only deliver 60Ah before reaching the recommended 50% DoD cutoff.

Temperature effects:

LiFePO4 capacity is reduced in cold temperatures but not catastrophically:

Charging below 0°C causes lithium plating on the graphite anode — a permanent and potentially dangerous degradation mechanism. A good BMS disconnects charging below 0°C. If you camp in genuinely cold conditions, either choose a battery with an integrated low-temperature cutout (most good ones do) or use a self-heating battery (Victron SmartLithium, Fogstar Drift Plus).

Sizing Your Battery: Worked Examples

Step 1: Calculate Your Daily Energy Use

List every appliance, its wattage, and daily hours of use. Convert to watt-hours (Wh) by multiplying watts × hours.

Example: typical full-time setup

Important: The 1,080Wh fridge figure is an average. A good compressor fridge at 20°C ambient temperature cycles on for about 50% of the time, drawing around 3–4A (36–48W) when running. This averages to ~45W. In summer heat, it might average 60–70W. Factor in the season you travel most.

Step 2: Calculate Required Battery Size

You need to store enough energy to get through a day (or more) without charging, with a buffer.

For a one-night autonomy target (no charging for 24 hours):

For LiFePO4 (80% usable depth of discharge):

Required capacity = Daily Wh ÷ voltage ÷ depth of discharge

= 1,925 ÷ 12 ÷ 0.80 = 200Ah

For AGM (50% usable depth of discharge):

= 1,925 ÷ 12 ÷ 0.50 = 321Ah → round up to 2× 200Ah AGM batteries

This illustrates why LiFePO4 wins on practicality: 200Ah LiFePO4 weighs ~22kg and costs ~£500. Two 200Ah AGM batteries weigh ~55kg each (110kg total) and cost ~£360 — plus you need a much bigger, heavier wiring setup to handle two batteries.

For two-night autonomy (important for UK winter when solar provides little):

LiFePO4: 1,925 × 2 ÷ 12 ÷ 0.80 = 400Ah (two 200Ah batteries)

Step 3: Add the Inverter Load

If you'll run 230V appliances through an inverter, add their consumption to your daily total. An inverter isn't 100% efficient — budget for 90% efficiency.

Example: running a Nespresso machine (1,100W) for 3 minutes per coffee, twice a day:

• 1,100W × (6 minutes ÷ 60) ÷ 0.90 efficiency = 122Wh additional per day

Example: running a laptop via 230V inverter vs 12V charger:

• 230V path: 65W adapter × 90% inverter efficiency = 72W actual draw from battery
• 12V path: 65W adapter at similar efficiency = ~70W draw from battery
• Difference is small; 12V USB-C is slightly more efficient but not dramatically

Step 4: Check Charging Can Keep Up

If your solar and DC-DC charger together can only replace 1,000Wh per day but you're using 1,925Wh, your battery will run down over multiple days. For sustainable off-grid use, your charging input must match or exceed your consumption. See our campervan charging systems guide for sizing the charging side.

UK Product Guide: Best Leisure Batteries 2026

LiFePO4 Batteries

Fogstar Drift (Budget–Mid Range)

Fogstar has become the go-to for value LiFePO4 in the UK. The Drift range uses prismatic cells (either EVE or CATL depending on batch), a 100A internal BMS, and Bluetooth monitoring via their app.

The 230Ah is exceptional value — more usable capacity than a 300Ah AGM setup at under a third of the weight.

Limitations: No low-temperature charging protection on standard Drift units. In winter, you'll need to ensure the battery is above 0°C before charging (the BMS doesn't automatically prevent it). The Fogstar Drift Plus (with heated cells) solves this.

Victron SmartLithium (Premium)

Victron's own LiFePO4 range integrates natively with their ecosystem. The SmartLithium batteries communicate over VE.Bus to a Cerbo GX or Venus GX, giving you full remote monitoring, automatic charging profile adjustment, and state-of-charge accuracy that standalone batteries can't match.

The SmartLithium 200Ah is the choice for Victron ecosystem builds. The native integration — where the MPPT, DC-DC charger, and battery all "talk" to each other — produces better charging behaviour and more accurate SoC than any combination of third-party equipment can achieve.

EcoFlow PowerKit Batteries

EcoFlow's modular system uses proprietary battery packs (2kWh units, expandable). These work well as part of their integrated system but are significantly more expensive per Ah and less flexible than standard LiFePO4. See all-in-one campervan power systems for a comparison.

SOK / Expion360

SOK batteries (made by the same Chinese manufacturer as many branded cells) offer competitive specs at lower prices than branded options. Available from specialist importers. No UK-based warranty support is the main drawback.

AGM Batteries (When They Still Make Sense)

For a weekend van where you're spending £400 on the whole electrical system and expect to sell the van in 3 years, a £85–£95 AGM makes sense. For anything used regularly, LiFePO4 wins on the 5-year cost calculation above.

LiFePO4 Cell Chemistry: What's Inside

Understanding what's actually inside your battery helps you make a better purchase decision.

Most LiFePO4 batteries sold for campervans use prismatic cells from two main Chinese manufacturers: EVE and CATL. These are the same manufacturers that supply major EV brands and battery storage systems.

A 200Ah battery typically uses four 50Ah prismatic cells (EVE LifePO4 50Ah is a common cell) wired in series to produce 12.8V nominal.

Grade A vs Grade B cells:

Cell manufacturers bin cells based on measured capacity and impedance. Grade A cells have capacity within ±3% of rated spec and low internal impedance. Grade B cells (also marketed as "Grade B Grade" or just sold as Grade A by less scrupulous sellers) may test at 90–95% of rated capacity or have higher impedance. Reputable UK sellers like Fogstar source Grade A cells; off-brand batteries from marketplaces are less predictable.

Prismatic vs cylindrical:

Prismatic cells are most common in campervan batteries. Cylindrical cells (like 18650s or 21700s) are used in some power stations and some imported batteries. Prismatic cells are easier to wire in parallel for high-capacity banks and have slightly better thermal properties in enclosed enclosures.

The BMS: What It Does and Why It Matters

Every LiFePO4 battery requires a Battery Management System (BMS). Without one, a LiFePO4 battery is genuinely dangerous — individual cells can over-charge or over-discharge to failure.

What the BMS monitors and controls:

• Cell balancing: Individual cells in a battery don't have perfectly identical capacity. Over hundreds of cycles, small differences accumulate and cells drift out of balance. The BMS applies a tiny balancing current to bring all cells to the same voltage during charging (passive balancing dissipates excess charge as heat; active balancing redistributes it). Without balancing, the weakest cell reaches full charge first and gets overcharged while the others are still charging.

• Over-voltage protection: Cuts charging if any cell exceeds 3.65V (full charge). Overcharging LiFePO4 risks capacity loss and, in extremes, cell rupture.

• Under-voltage protection: Cuts discharge if any cell drops below 2.5–2.8V (empty). Over-discharging causes permanent capacity loss.

• Over-current protection: Limits maximum discharge current. A 100A BMS will disconnect the battery if discharge exceeds 100A — protecting both cells and wiring.

• Short-circuit protection: Disconnects within milliseconds of a dead short. This is critical — LiFePO4 can deliver enormous fault currents.

• Temperature protection: Disconnects charging below 0°C (prevents lithium plating) and both charging and discharging above 60–70°C (prevents thermal damage).

BMS trip — what happens:

When a BMS trips on over-discharge, it disconnects the output. Your fridge, lights, and everything else goes off. To reset, you need to apply a charging voltage (connect solar, a charger, or drive with DC-DC active). Most BMS units auto-reset once voltage returns.

If your battery shuts off unexpectedly and won't come back on, the likely causes are:

1. Over-discharge (charge the battery)
2. Over-temperature (let it cool)
3. Cell imbalance causing premature over-voltage trip (do a full charge cycle; the BMS will balance)

Internal vs external BMS:

Most consumer LiFePO4 batteries (Fogstar, Victron SmartLithium, etc.) have the BMS integrated inside the battery case. DIY builders using raw prismatic cells add an external BMS (JK BMS, Daly, Overkill Solar) mounted separately. External BMS offers more configuration options but requires more assembly knowledge. See DIY LiFePO4 battery guide for the complete process.

Battery Bank Configurations

Single Battery

The simplest configuration. All charge sources and loads connect to one battery. Suitable for most builds.

Two or More Batteries in Parallel (Higher Capacity)

Wiring two identical LiFePO4 batteries positive-to-positive and negative-to-negative doubles your Ah capacity while keeping the same 12V nominal voltage.

Critical rule: Only parallel identical batteries — same manufacturer, same model, same capacity, same age. Paralleling different batteries causes large equalisation currents that can damage both the batteries and the BMS units.

Wiring a parallel bank correctly:

Use equal-length cables from each battery to the bus bar. Unequal cable lengths cause unequal resistance, meaning one battery does most of the work. The accepted method is to use two identical cables and connect them at a common bus bar, not battery-to-battery-to-bus-bar in a chain.

Two batteries with internal BMS units can be connected in parallel. The BMS units will operate independently; if one battery's BMS trips, the other continues supplying the system.

Two Batteries in Series (24V System)

Wiring two 12V batteries positive-to-negative-to-positive doubles the voltage to 24V while keeping the same Ah capacity. Used for large builds (300Ah+) where the lower current at 24V allows thinner cables.

A 24V system requires a 24V inverter, 24V MPPT controller, and 24V-to-12V DC converter for 12V loads. The additional complexity is rarely worth it below 300Ah. See 12V vs 24V campervan electrical systems for the full trade-off analysis.

Understanding Amp-Hours vs Watt-Hours

Amp-hours (Ah) is a measure of charge, not energy. A 100Ah battery at 12V stores 1,200Wh. The same 100Ah at 24V stores 2,400Wh. When comparing batteries or calculating run times, always convert to Wh to avoid confusion.

Conversion formula: Wh = Ah × Voltage

Installation: Placement, Mounting, and Wiring

Where to Mount the Battery

The best location balances cable length (shorter is better for efficiency and cost), weight distribution (low and central), and access for inspection.

Common locations:

• Under a fixed bed (aft): Most popular. Low centre of gravity, keeps weight over the rear axle, close to where most loads are. Downside: not always easy to access.

• Under the passenger seat: Common in vans with limited floor space. Short cable run to the front for DC-DC charger. Ensure ventilation — though LiFePO4 generates minimal gas, the BMS produces some heat during charging.

• Garage/floor beneath a lifted floor: Clean installation, good access, but requires longer cable runs.

What to avoid:

• Engine bay (too hot)
• Directly against the wheel arch (road spray, temperature extremes)
• Any location where the battery cannot be properly secured

Securing the Battery

A 20kg LiFePO4 battery in a crash can become a projectile. Mount it so it cannot move in any direction — forward, back, left, right, and upward.

Use purpose-made battery boxes, or fabricate a steel or aluminium frame. Use threaded rod or bolts into the van floor (through the floor into existing structural members, sealed with silicone). Battery terminal covers should be in place whenever the van is in motion.

For prismatic cells without a plastic case, use a metal battery box — the compression also maintains cell health (prismatic cells expand slightly during charging; compression prevents them from warping over time).

Cable Sizing for the Main Battery Circuit

The cable between your battery and the main positive bus bar carries the entire system's current. Size it generously.

Use flexible, fine-stranded (Class 5 or Class 6) copper cable — not rigid house wire. Marine-grade or automotive-grade cable with tinned copper conductors resists corrosion. Use ring terminals crimped with a proper ratchet crimper — never rely on soldering alone.

The ANL fuse:

The main positive cable must be fused within 300mm of the battery positive terminal. This is the most important fuse in the system — it protects against a direct short anywhere in the main wiring. Use an ANL fuse (bolt-through fuse) in an ANL fuse holder.

Size the ANL fuse at the maximum current your cables can carry, not the expected system load:

Commissioning Sequence

Connect in this order to avoid sparks and accidents:

1. Connect negative bus bar to battery negative (no current flows — negative path only)
2. Connect all loads and charge sources to the bus bars (still no current — ANL fuse not inserted)
3. Verify all connections are tight; check polarity of every component
4. Insert ANL fuse — system goes live
5. Check voltage at bus bars with a multimeter (should read battery voltage)
6. Switch on circuits one by one and verify each works

Never insert the ANL fuse until all other connections are made. This prevents a scenario where a misconnected wire shorts to chassis while you're crimping the next connection.

Battery Monitoring

You cannot accurately know the state of charge of a LiFePO4 battery from voltage alone. The flat discharge curve means voltage stays at ~13.2V from 90% down to 10% SoC — voltage is a poor indicator until the battery is nearly empty.

A battery monitor (or coulomb counter) tracks every amp flowing in and out, integrating over time to calculate SoC accurately. This is essential for informed power management.

Victron SmartShunt 500A:

The most popular choice for campervan builds. A precision shunt resistor (typically 500A/50mV) is inserted in the main negative cable. The SmartShunt measures voltage across the shunt to calculate current, then integrates to track SoC. Communicates via Bluetooth to the Victron app.

Installation: the SmartShunt goes in the main negative cable between the battery negative terminal and the negative bus bar — every amp in and out passes through it.

Settings to configure:

• Battery capacity: Set to the actual rated Ah of your battery
• Charge voltage: Set to your charger's absorption voltage (14.2–14.4V for LiFePO4)
• Tail current: The current level at which the battery is considered "full" (typically 4% of capacity — 8A for a 200Ah battery)
• Peukert exponent: For LiFePO4, set to 1.05 (nearly 1.0 — the Peukert effect is minimal)
• Charged detection time: 3 minutes at tail current before marking as 100%

Alternative: Victron BMV-712

The BMV-712 is the standalone battery monitor version — a dedicated display unit rather than app-only. Better if you want a permanent dashboard. Uses the same shunt measurement principle.

Integrating with Victron ecosystem:

If you have a Cerbo GX (Victron's communication hub), it pulls data from the SmartShunt, SmartSolar MPPT, Orion-Tr DC-DC charger, and displays everything in one place. Remote access via VRM (Victron Remote Management) lets you see your battery SoC from a phone anywhere in the world.

Charging Profiles: Getting the Most From Your Battery

LiFePO4 batteries charge in two stages:

Bulk/Absorption phase: The charger delivers maximum current until cell voltage reaches the absorption target (~14.2–14.4V for a 12V LiFePO4). This fills the battery to approximately 95%.

Float/Storage phase: LiFePO4 does not require a float voltage the way lead-acid does. Many quality chargers and charge controllers disable float for LiFePO4, or set it at a low voltage (13.2–13.5V) just to compensate for self-discharge.

Why you shouldn't always charge to 100%:

LiFePO4 cells experience slightly more stress at full charge (all lithium ions on the graphite anode, under maximum tension). For maximum cycle life, some builders set absorption voltage to 14.0V rather than 14.4V, which charges to ~97% SoC rather than 100%. The trade-off is a small reduction in usable capacity.

For most campervan use, 14.2–14.4V absorption and no float is the recommended setting — it balances cycle life against usable capacity.

Absorption voltage settings by chemistry:

Every charge source (MPPT controller, DC-DC charger, mains charger) must be set for the correct chemistry. A charger set for AGM will incorrectly apply a higher absorption voltage to LiFePO4, potentially damaging the cells over time.

Battery Health and Maintenance

LiFePO4 Maintenance

LiFePO4 requires minimal maintenance:

• Check cell balance: Most BMS apps display individual cell voltages. Healthy cells stay within 20–30mV of each other during charging. If one cell consistently reads high or low, the battery may need a full charge-discharge cycle to allow balancing, or the BMS may have a weak balancer.

• Clean terminals: Inspect twice a year. Copper terminals oxidise slowly; light oxidation is normal. For severe corrosion, clean with a wire brush and apply anti-corrosion spray or petroleum jelly.

• Check mounting: Verify the battery hasn't shifted in its mount. Check all battery cable connections for looseness.

• Capacity test: After 2–3 years of use, do a full capacity test. Charge to 100%, then discharge at a known rate (e.g., 20A constant via a load or normal usage) and measure total Ah discharged. Compare to rated capacity. Capacity below 80% of rated indicates significant degradation.

Winterising LiFePO4

LiFePO4 needs less attention in winter storage than AGM:

1. Bring the battery to 50–60% SoC (resting voltage approximately 13.2–13.3V)
2. Disconnect from all loads and chargers
3. Store anywhere above -20°C — a cold garage is fine for LiFePO4 in storage (not charging)
4. No maintenance charger required — 1–3% self-discharge per month means a battery stored at 55% SoC in October will still be above 40% SoC in April

In spring, reconnect, do a full charge-discharge cycle to recalibrate the battery monitor, and check BMS logs via the app for any fault history.

See winterising your leisure battery for the complete seasonal guide.

Winterising AGM

AGM needs more attention:

1. Charge fully before storage (absorption charge to 14.4–14.7V until current drops below 2A)
2. Connect a maintenance charger (CTEK MXS 5.0 is the standard recommendation — £55 from most car accessory shops). This delivers a tiny pulse charge every few weeks to offset the 3–5% monthly self-discharge
3. Check voltage every 6 weeks; recharge if it falls below 12.4V (50% SoC)
4. Keep in a cool (5–15°C), dry location
5. Never allow AGM to freeze — a discharged AGM can freeze at -15°C, cracking the plates

Troubleshooting Common Battery Problems

Battery drains overnight despite nothing being on:

Measure with a clamp meter or multimeter in series on the negative cable. Anything above 50mA (0.05A) with everything switched off is a parasitic drain. Common culprits: inverter on standby (5–20W), fridge drawing on its own wake cycle, solar controller's parasitic load (most modern MPPT controllers draw less than 10mA).

Battery monitor shows incorrect SoC:

Battery monitors drift over time, especially if the battery was ever deeply discharged or overcharged. Recalibrate: charge the battery fully (let the charger complete its full cycle, including absorption phase with current tapering), then reset the battery monitor's SoC to 100%. The monitor will start recounting from known full.

Battery won't charge from solar:

Check the chain: solar panels → MPPT controller → battery. Verify panel voltage and current at the MPPT input (should be above battery voltage, typically 15–20V per 12V panel). Check the MPPT output voltage (should be at or near absorption voltage on a sunny day). If MPPT output is correct but battery isn't accepting charge, the battery BMS may have disconnected due to over-temperature or a fault.

BMS keeps tripping:

If the BMS trips repeatedly, check:

1. Discharge rate too high (you're drawing more current than the BMS rating)
2. Cell imbalance — one cell hitting overvoltage trigger during charge
3. Temperature — BMS tripping on overtemperature
4. Genuine battery fault — a failed cell will consistently trip the BMS at the same SoC point

Batteries in parallel not sharing load equally:

Check that both batteries are the same type, same age, and at the same SoC before paralleling. Measure voltage of each battery individually; if one is significantly lower, charge it separately to match the other before connecting. Ensure cable lengths are equal.

Second-Hand LiFePO4 Batteries: Risks and Opportunities

Used LiFePO4 can be bought for 40–60% of new price from online marketplaces, ex-off-grid solar systems, or EV battery salvage. The risks:

• Unknown cycle count: You have no way to verify how many cycles a used battery has done. The seller's word is the only evidence.
• Cell imbalance: Old batteries may have cells at significantly different SoC, requiring a long balancing cycle before they're accurate.
• BMS condition: External BMS units in DIY builds may have faults that aren't immediately apparent.
• Capacity degradation: Test capacity (charge fully, discharge to cutoff at a known rate) before paying; accept only batteries above 80% of rated capacity.

For a budget first van, used LiFePO4 is a reasonable option if you can verify capacity. For a build you'll rely on daily, buy new.

Related Guides

• Campervan solar setup guide — how to charge your battery from the sun
• Campervan charging systems guide — DC-DC, shore power, and alternator charging
• Campervan wiring & safety guide — wire gauges, fuses, and safety
• Campervan inverters guide — running 230V appliances from your battery
• Campervan electrical system guide — the complete overview

FAQ

What size leisure battery do I need for a campervan?

For weekend use with basic appliances (lights, fridge, USB charging): 100Ah LiFePO4 is usually sufficient. For full-time van life with a laptop, diesel heater, and regular usage: 200Ah LiFePO4 is the sweet spot. For heavy usage including daily inverter use or induction cooking: 300Ah+ LiFePO4. Use the sizing calculation above for a precise figure based on your actual appliances.

LiFePO4 vs AGM — which should I choose?

For any van used more than a couple of weekends per month, LiFePO4. The higher upfront cost is recovered within 2–3 years through longer battery life. The weight saving (half the weight) is also significant for handling and fuel economy. AGM only makes sense for a very low-budget first build you expect to upgrade soon.

Can I use a car battery as a leisure battery?

No. Car batteries (starter batteries) are designed to deliver very high current for a short burst (starting the engine), then be recharged immediately by the alternator. Deep cycling them — drawing them down over hours — permanently damages the plates within weeks. Always use a proper deep-cycle leisure battery.

How long does a LiFePO4 leisure battery last?

Quality LiFePO4 batteries (Grade A cells, quality BMS) are rated for 3,000–5,000 cycles to 80% capacity. At one cycle per day (daily full discharge and charge), this is 8–14 years. Most campervan batteries won't see daily full cycles — they'll last longer in practice. The cycle life guarantee from reputable manufacturers is typically 2,000–3,000 cycles in writing.

Can I mix different battery brands in parallel?

No. Only parallel identical batteries — same manufacturer, model, capacity, and ideally age. Mixing creates voltage imbalances during charging and discharging that can damage both batteries, and may cause large equalisation currents between batteries with different internal BMS logic.

Does a LiFePO4 battery need a maintenance charger in winter?

No. LiFePO4 self-discharges at only 1–3% per month. A battery stored at 50% SoC in October will still have usable charge in March with no intervention. Store it, leave it, reconnect it in spring.

What happens when a LiFePO4 BMS trips?

The battery disconnects its output — your van goes dark. To reset, you need to apply a charging voltage (connect shore power, start the engine with DC-DC charger active, or ensure solar panels are producing). The BMS will automatically reconnect once it detects a valid charge voltage. If the BMS trips repeatedly, something is wrong — see the troubleshooting section above.

Is a 200Ah LiFePO4 better than a 200Ah AGM?

The 200Ah LiFePO4 gives you 160–180Ah of usable capacity. The 200Ah AGM gives you 100Ah usable. At 12V, that's 1,920–2,160Wh vs 1,200Wh — 60–80% more usable energy from the same nominal Ah, at half the weight, with 10× the cycle life.