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Doubling your battery bank by adding a second battery in parallel is the most common upgrade in van life. Two 100Ah batteries in parallel give you 200Ah at the same 12V — twice the capacity, same voltage. But wire it wrong and you'll kill both batteries within a year.
The golden rule of parallel batteries: same brand, same model, same age, same capacity. Mixing a new battery with a 2-year-old one forces the new battery to constantly compensate for the older one's higher internal resistance. The new battery works harder, heats up more, and degrades to match the old one within months. If you can't buy two identical batteries at the same time, don't parallel them.
⚡ Expert tip
Before connecting two batteries in parallel, charge both to exactly the same voltage independently. If battery A is at 13.2V and battery B is at 12.8V, connecting them causes a massive inrush current as they equalize — potentially damaging the BMS or welding your terminal connections. Charge both to 13.3V, then connect.
Example calculation for your setup
Results based on a typical use case
| Appliance | Power | Usage/day | Wh/day |
|---|---|---|---|
| Compression fridge | 45W | 24h | 1080 |
| LED lighting | 20W | 4h | 80 |
| Water pump | 30W | 0.5h | 15 |
| Phone charging | 15W | 2h | 30 |
| Daily consumption | 1205 Wh | ||
Recommended LiFePO4 battery
126 Ah
(80% depth of discharge)
Recommended AGM battery
201 Ah
(50% depth of discharge)
Recommended solar panels
302 Wc
4h average sun hours
Recommended inverter
No 220V appliances — no inverter needed
Adjust these values with the calculator below
VANPOWERCALC PROYOUR ENERGY PROFILE
YOUR ENERGY PROFILE.
This document contains the sizing of your future electrical installation, calculated based on your appliances.
Minimum Daily Consumption
0 WH / DAY
Inventory:
SYSTEM SIZINGPage 2
Battery
To guarantee 0WH without damaging your bank (80% max discharge):
0 AH
LiFePO4 12V
Solar
Minimum power required to recharge your consumption:
0 W
via MPPT
220V AC
Maximum power (with 25% safety margin).
0 W
No Need
Safety & CablingPage 3
12V Cable Sizing Guide
Use this professional reference table to select the correct gauge (mm²) for your cables. For 12V in a van, the maximum tolerated voltage drop is 3%. Always use multi-stranded flexible automotive wire.
| Current (A) | Round trip < 2m | Round trip 4m | Round trip 6m |
|---|---|---|---|
| 5A (LEDs, USB) | 1.5 mm² | 2.5 mm² | 4 mm² |
| 10A (Fridge, Pump) | 2.5 mm² | 4 mm² | 6 mm² |
| 20A (Heater) | 4 mm² | 10 mm² | 10 mm² |
| 50A (DC/DC Booster) | 10 mm² | 16 mm² | 25 mm² |
| 100A (Inverter) | 25 mm² | 35 mm² | 50 mm² |
Fuse Sizing
The fuse protects the wire, not the appliance. Always place it as close to the power source as possible (battery or busbar).
- Wire 1.5 mm² → Max fuse 10A
- Wire 2.5 mm² → Max fuse 20A
- Wire 4 mm² → Max fuse 30A
- Wire 6 mm² → Max fuse 40A
- Wire 10 mm² → Max fuse 60A
SCHÉMA ÉLECTRIQUE
PANNEAUX SOLAIRES
0W
REGULATEUR MPPT
BATTERIE AUXILIAIRE
0 Ah
Lithium LiFePO4
FUSIBLE
FUSIBLE
BOÎTE À FUSIBLES 12V
Pompe, Leds, Frigo...
CONVERTISSEUR 220V
NON REQUI
PRO GEARPage 4
SHOPPING LIST
Where to find this equipment? Here is the community-approved selection.
12V 6-way Fuse Box
Mandatory protection
Digital Multimeter
Test your connections
Heavy Duty Crimping Tool
For perfect lugs
Heat Shrink Tubing
Insulation and safety
GENERATED BY VANPOWERCALC PRO - UNLIMITED.
About this tool
Wiring matters more than people think. Connect both batteries with equal-length cables to a common bus bar — not daisy-chained (battery 1 → battery 2 → load). Daisy-chaining means battery 1 handles more current because it's closer to the load, leading to uneven wear. Equal-length cables ensure both batteries share the load 50/50. Use 25mm² (4 AWG) minimum for the interconnects on 200Ah systems, with a fuse on each battery's positive cable before they merge at the bus bar. I use 60A ANL fuses on each 100Ah battery — rated to protect the interconnect cable, not the battery capacity. One more thing: if you're paralleling LiFePO4 batteries with separate BMS units, make sure both BMS chips are compatible with parallel operation. Some cheaper BMS units fight each other — one cuts off while the other tries to compensate, creating a voltage oscillation that can trip both. SOK and BattleBorn are explicitly rated for parallel. Check the spec sheet for any others.
Frequently asked questions
Can I mix different battery brands in parallel?▼
Strongly not recommended. Different internal resistances cause uneven current sharing — one battery works harder and ages faster. Same brand, same model, same age, same capacity. If you already have a 100Ah Renogy and want to add capacity, sell it and buy two matched batteries.
What cable size for parallel battery connections?▼
25mm² (4 AWG) minimum for 200Ah systems, 35mm² (2 AWG) for 300Ah+. The interconnect cables carry the full current from one battery to the bus bar. Undersized cables create a resistance imbalance that defeats the purpose of paralleling.
Do I need a fuse between parallel batteries?▼
Yes — one fuse on each battery's positive cable before they meet at the bus bar. If one battery develops an internal short, the fuse prevents the other from dumping its entire capacity into the fault. 60A ANL for 100Ah batteries, 100A for 200Ah.
How many batteries can I parallel?▼
Practically, 2-4 batteries in a van. Beyond 4, current imbalances become hard to manage without active balancing. For very large banks (600Ah+), consider fewer larger batteries rather than many small ones.
Can I parallel LiFePO4 and AGM?▼
Never. Different charge voltages (14.6V vs 14.4V), different internal resistance, different discharge curves. One will overcharge while the other undercharges. This can cause thermal runaway in AGM or BMS lockout on LiFePO4. Same chemistry only.