This guide is for unattended, outdoor Meshtastic nodes using one or two 18650 lithium-ion cells with a 3.7V system. ABS enclosures are intentionally excluded due to fire risk.
(1–2x 18650, 3.7V, 8x8x6 enclosure — STEEL ONLY)
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1. Enclosure Selection (Revised)
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Steel NEMA Enclosure (Required)
- Will not melt or drip if a cell vents or fails
- Better at containing flame and debris
- Preferred for mounting on poles, buildings, or structures
- Must be properly grounded
Notes:
- Steel is safer but can retain heat if sealed
- Internal airflow and thermal planning still matter
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2. Enclosure Venting (Important)
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Yes, a vent is recommended — but it must be done correctly.
Why venting helps:
- Reduces heat buildup from sun exposure
- Prevents pressure buildup if a cell vents gas
- Extends battery life in hot environments
What NOT to do:
- Do not drill an open hole
- Do not leave the enclosure unsealed
- Do not rely on venting alone for safety
Best vent options:
- Gore-style pressure equalization vent
- NEMA-rated breather vent (IP66 / IP67 rated)
- Small stainless or aluminum vent with hydrophobic membrane
Vent placement:
- Upper side wall or near the top (hot air rises)
- Not directly above the battery pack
- Avoid sun-facing walls if possible
Result:
- Allows gas and pressure to escape
- Blocks rain, insects, and dust
- Significantly reduces internal temperature swings
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3. Fire-Resistant Battery Containment
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Strongly recommended even with a steel enclosure.
- Place batteries in a Li-ion / LiPo fire-resistant bag or sleeve
- Slows flame spread and heat transfer
- Provides a second containment layer
- Do NOT seal airtight inside the bag
Think of this as a seatbelt, not a roll cage.
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4. Battery Configuration
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Number of cells:
- 1 cell: lowest complexity and risk
- 2 cells: PARALLEL ONLY (still 3.7V)
Rules:
- Same brand, model, and age
- Never mix old and new cells
- Avoid reclaimed or unknown cells
Avoid:
- Series configurations
- DIY spot-weld packs unless you know what you’re doing
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5. Recommended 18650 Cell Types
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Use reputable cells only:
- Samsung INR18650-30Q
- Panasonic / Sanyo NCR18650GA
- Molicel M35A or P28A
If compatible with your holder:
- Protected button-top cells add over/under-voltage protection
- Verify length clearance before buying
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6. Charging and Power Control
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RAK Built-In Controller
- Suitable for 1S (single-cell) Li-ion charging
- Designed for intermittent solar input
- Ensure termination voltage is 4.2V max
External Controller Options (1S Li-ion):
- BQ24074 / BQ24075
- MCP73871
- CN3065 (from reputable vendors only)
Never:
- Connect solar panels directly to cells
- Use unknown charge modules
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7. Electrical Protection
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Required:
- Inline fuse or polyfuse on battery output
Recommended:
- Low-voltage cutoff (if not built in)
- Temperature sensing if supported
This prevents wiring faults from becoming battery events.
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8. Thermal Management
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- Shade the enclosure whenever possible
- Use light-colored or reflective finishes
- Mount batteries away from sun-facing walls
- Use venting to reduce heat soak
- Avoid fully sealed steel boxes with no airflow
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9. Recommended Best-Practice Setup
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Preferred configuration:
- Steel NEMA enclosure
- NEMA-rated breather vent
- 1–2 matched 18650 cells in parallel
- Fire-resistant battery bag
- Proper Li-ion solar charge controller
- Inline fuse or polyfuse
- Shaded mounting location
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10. Final Notes
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Most real-world battery incidents come from:
- Overcharging
- Excessive heat
- Poor-quality cells
- Lack of basic electrical protection
A steel enclosure with venting, quality cells, and
conservative charging is very close to commercial
outdoor sensor and radio deployment standards.
Reputable 18650 Cells — Typical Cost Per Cell (USD)
Cell / Model | Type | Vendor | Cost | Link
-----------------------+-----------------------+-------------------+-------+--------
Samsung 30Q | Flat-top, unprotected | 18650BatteryStore | $3.05 | Link
Samsung 30Q | Flat-top, unprotected | 18650Battery.com | $4.99 | Link
Molicel P28A (2800mAh) | Flat-top, unprotected | 18650BatteryStore | $2.45 | link
Molicel P28A (2800mAh) | Flat-top, unprotected | IMR Batteries | $4.99 | Link
Molicel P30B (3000mAh) | Flat-top, unprotected | 18650BatteryStore | $4.49 | Link
Molicel P30B (3000mAh) | Flat-top, unprotected | 18650Battery.com | $4.99 | Link
Sanyo NCR18650GA | Flat-top, unprotected | BatteryWorld | $5.06 | Link
Nitecore NL1836HP | Button-top, protected | IMR Batteries | $19.95| Link
Fenix ARB-L18-3500 | Button-top, protected | OnRope1 (Fenix) | $24.95| Link