Building a Camping LiFePO4 Battery

This article covers building a portable 12V LiFePO4 battery with 110Ah capacity in a suitcase case for camping and car tourism. The author shares five years of experience using a backup power source for powering a campsite.

Power Consumers at Camp

Total daily consumption varies from 20 to 40 Ah and includes:

• Charging devices: flashlights, phones, radios (car USB ports draw 3-7A even without ignition)
• Lighting: 8-20 watts (an 8W floodlight + two 10W COB lights)
• Heating: diesel autonomous heaters 2-5 kW (10A at startup, 0.5-2.5A during operation)
• Refrigerator: minimum 15Ah per day
• Food warming: 12V multicooker and 120W electric thermal mug

Choosing a Solution

Out of four options (gasoline generator, solar panels, no solution, separate lithium battery), the author chose the last option as the most practical for extended stays.

Components for the New Build

• Battery cells: 4x EVE LF105AH (actual capacity 110-115Ah) — 11,000 rubles
• BMS: Daly 150A 4-8S blue — 3,300 rubles (blue version chosen for built-in balancing and Bluetooth)
• Case: plastic suitcase with handle — 1,300 rubles
• USB charger: 140-watt module with heatsink — 600 rubles
• Bidirectional charging module: IP2368 at 140 watts — 700 rubles
• Step-up DC-DC converter: small board — 350 rubles
• Built-in connectors: 2x Type-C and 1x USB-A, sealed — 2,300 rubles
• Cigarette lighter socket, XT90 and XT60 connectors, connection button — ~300 rubles each
• Thermal insulation and heating: polystyrene foam, seat heating mat, controller — ~600-900 rubles total
• Other materials: fiberglass PCB material, wires of various gauges (6, 7, 8 AWG for power), terminals, stainless screws, tape, carpet

Critical Discovery About USB Chargers

Built-in 12V USB chargers claim up to 140 watts of power, but deliver only 15-18 watts from a 12V input. They only reach full power at 24V input voltage. The solution: install a step-up DC-DC converter inside the case to boost voltage to 24V. Then the output reaches 110+ watts.

Battery Management System (BMS)

The Daly BMS performs these functions:

• Overcharge and over-discharge prevention
• Protection against excessive discharge current
• Cell balancing (built into the blue version)
• Communication with external devices via CAN, RS485, UART, Bluetooth, Wi-Fi
• Heating control via separate module
• Maximum voltage limiting (14.2V recommended instead of standard 14.6V to extend lifespan)

Construction Decisions

Module power distribution system: Instead of running many wires from the battery pack, a "T-splitter" was created from fiberglass PCB material with a single connection point (+) on the battery. All modules on the electronics plate connect through two screw terminals (+ and -).

Thermal insulation: Three layers — 3mm polystyrene foam on top and bottom, carbon-fiber heating mat, carpet. Size is limited to the 11mm of free space between the cells and the suitcase lid.

Protection: A 1mm fiberglass plate between the front wall and the assembly prevents short circuits from exposed connector contacts during mechanical damage (fire safety).

Connector placement: XT90 and XT60 on the front wall (inside the handle and under the latch), USB and cigarette lighter socket on the side. Sealed connectors with short pigtails are installed.

Assembly Process

1. Cell preparation: 0.5mm fiberglass sheets placed between cells, everything taped together as a single module
2. Height measurement: a plasticine ball under the closed lid showed 11mm of free space
3. Mounting system: a 2mm fiberglass plate becomes the frame for all electronics
4. XT connector soldering: wires soldered at 90 degrees due to limited space; half-tubes of connectors used, which can be rotated for convenience
5. Wire crimping: hydraulic press with crimping tool dies was used
6. Interior finish: the wife covered the inside of the case with self-adhesive carpet
7. Density problem: the purple bidirectional charging board didn't fit in the planned location due to connectors; solution — placement on top of the fiberglass plate on plastic zip ties
8. Power button: installed in the center of the front wall (replacing the pressure relief valve); configured via BMS-Tool software under Manufacturing, Key logic
9. Electronics sealing: all small components (inductors, resistors, heatsinks, capacitors) glued with sealant

Testing

• From phone charger (bidirectional module): stable 56 watts
• From car charger via XT60: full 140-watt power
• Charging a fully discharged battery: approximately 1.5 hours at 30A

The Physics of Heating

LiFePO4 batteries cannot be charged at negative temperatures (except special "winter" versions). When cooled, voltage drops, creating risk of overcharging during thawing and degradation. The heating system maintains temperature above 0 degrees C, switching off at +5 degrees C.

Final Costs

Parts cost 20,000-25,000 rubles (excluding tools and consumables). The previous five-year-old version (55Ah in a plywood case) fully justified itself in field conditions, including use with a boat electric motor.