Buying a camper battery based on amp-hours alone is how most people end up with the wrong one. The headline number tells you rated capacity. It does not tell you how much of that you can actually use, how the battery behaves at 0C, whether your alternator or solar setup can charge it properly, or how long it will last after 400 cycles. Those details vary significantly between chemistries and even between products in the same category.
This guide covers the specs that matter when comparing auxiliary batteries for campervans, RVs, and overlanding setups.
Quick answer
For light weekend use with a fan, LED lights, and phone charging, a 100Ah lithium or 120Ah AGM gets through one or two nights without a problem. A 12V compressor fridge running continuously changes the math. A 60-litre compressor fridge draws roughly 30-50Ah per day depending on ambient temperature. Add a laptop and occasional inverter use and you are looking at 80-120Ah of daily draw. That is where 200Ah starts making sense.
Lithium is lighter, delivers more usable capacity per Ah rated, and handles high charge and discharge rates better than AGM. The Renogy 12V 200Ah LiFePO4 is one product buyers frequently compare in this segment. Verify the current spec sheet directly with Renogy before purchasing; dimensions and BMS specs can change between production runs.
Specifications
| Parameter | AGM | LiFePO4 (Lithium) |
|---|---|---|
| Common sizes | 100Ah, 120Ah, 200Ah | 100Ah, 200Ah |
| Typical use case | Budget builds, occasional weekend use | Full-time van life, overlanding, heavy loads |
| Usable capacity | ~50% of rated Ah | 80-100% of rated Ah |
| Weight (200Ah typical) | 55-65 kg | 22-26 kg |
| Bulk charge voltage | 14.4-14.8V | 14.2-14.6V |
| Low-temp charging | OK to around -20C | Stops below 0C without heated BMS |
| Cycle life | 200-500 cycles at 50% DoD | 2,000-5,000+ cycles at 80% DoD |
| Max continuous discharge | C/5 typical | C/1 or higher, model dependent |
| Inverter compatibility | Yes, size limits apply | Yes, better at sustained high draw |
| Fitment | Standard group sizes widely available | Varies by brand; measure before ordering |
Usable capacity figures assume proper charging. Real-world performance varies with temperature and battery age. Cycle life is manufacturer-typical. Heated BMS is a specific feature, not universal across LiFePO4 products.
How to choose the right spec
Start with load, not battery size.
Add up what you actually run. A compressor fridge, a USB charger, and an LED strip are a manageable daily draw. Add a 1000W inverter for a coffee maker twice a day and you need to rethink both capacity and your charging source at the same time.
100Ah vs 200Ah. A 100Ah LiFePO4 gives you 80-100Ah usable. A 100Ah AGM gives you roughly 50Ah before you start shortening its life. If your daily draw is 60Ah or more and you have limited solar or short driving windows to recharge, 200Ah lithium is the practical choice. A 200Ah AGM weighs around 60 kg, takes most of a day to recharge from a single 200W panel, and degrades faster under daily cycling.
AGM vs lithium. AGM is cheaper to buy. Lithium costs more and lasts longer under real use. For a van driven daily with solar and alternator charging, lithium pays back over three or four years of use. For a trailer used six weekends per year, AGM may be the more sensible call.
Fitment. Measure your battery box before ordering. 200Ah lithium batteries vary more in physical dimensions than AGM. A Renogy 200Ah LiFePO4 has different dimensions than a Battle Born or a Victron equivalent. Do not assume they are interchangeable.
Charging setup. Lithium requires a charger or DC-DC converter with a lithium-specific charging profile. Running a LiFePO4 on an AGM-profile charger will not destroy it immediately, but it will consistently undercharge the battery. A proper DC-DC charger is not optional if you are alternator-charging a lithium bank.
Future upgrades. If you plan to add a second battery later, choose a chemistry now that scales. Mixing AGM and lithium in parallel is not recommended.
How to check
- Confirm physical dimensions before ordering. Width, length, height, and terminal position. All four.
- Verify nominal voltage. Most camper setups are 12V. Some larger RV systems run 24V. They are not interchangeable.
- Check charger compatibility. Does your shore power charger, solar charge controller, and DC-DC unit each have a LiFePO4 charging profile? If any one of them does not, your battery will not charge correctly.
- Confirm low-temperature charging behavior. LiFePO4 batteries without a heated BMS will refuse to accept charge below 0C. The battery will still discharge, but it will not charge until it warms up. If you camp in winter, this matters.
- Check usable capacity, not just rated Ah. A 200Ah AGM used to 50% depth of discharge gives you 100Ah. A 100Ah LiFePO4 used to 90% gives you 90Ah. The real-world gap between the two is smaller than the headline numbers suggest.
- Confirm the alternator charging path. A DC-DC charger protects the alternator and charges the aux battery correctly. Confirm it is rated for your battery size and chemistry.
- Read the current warranty document. Terms and coverage change between product generations. Check the manufacturer’s current documentation, not a review from two years ago.
What goes wrong
Buying based on Ah alone. A 200Ah AGM and a 200Ah LiFePO4 are not the same product. Usable capacity, weight, cycle life, and charging requirements are all different. Choosing the cheaper one without accounting for those differences is the most common mistake in this category.
Ignoring weight and fitment. A 200Ah AGM weighs around 60 kg. Mounted under a bed behind a panel, it becomes a real problem if it ever needs to move. Dimensions also matter; people order first and measure second, then find the battery does not fit the compartment.
Incompatible charging gear. The battery arrives, connects to an existing AGM setup, and never fully charges. That is not a battery defect. It is a charger profile mismatch. Fix the charger before assuming the battery is faulty.
Assuming all lithium behaves the same in cold. Some LiFePO4 batteries include a built-in heater that activates during charging at sub-zero temperatures. Many do not. If you park in cold locations and expect to start charging from solar at sunrise in January, you need to know which type you have.
Overestimating runtime. Battery capacity decreases with age. Fridge draw increases in warm weather. Inverter efficiency eats into available power. People calculate runtime under ideal conditions and are surprised when real results come in shorter. Build in a 20-30% margin on your load estimates.
Choosing 200Ah when the charging system cannot keep up. A 200Ah LiFePO4 wants 40-100A of charge current to fill in a reasonable time. A single 100W panel and a stock alternator with no DC-DC charger will not keep up with heavy daily use. The battery is not the bottleneck there. The charging system is.
Sources
- Renogy — product documentation and BMS spec sheets
- Victron Energy — Battery FAQ and Wiring Unlimited technical guide
- Battle Born Batteries — technical support documentation
- Trojan Battery — AGM cycle life and technical specifications
- ABYC E-11 and E-13 DC electrical system standards (referenced for 12V system design)
