This project uses lithium thionyl chloride (Li-SOCl₂) primary cells. These are extremely safe when used correctly and capable of causing serious injury or fire when used incorrectly. Read this before handling cells.

Li-SOCl₂ cells contain:

• Lithium metal (flammable on contact with water)
• Thionyl chloride (SOCl₂) electrolyte — corrosive, reacts violently with water to produce sulfur dioxide and hydrogen chloride gas

A damaged, shorted, or overheated cell can:

• Vent flammable/corrosive gases
• Catch fire
• Explode (rare, but possible with mechanical violence)

• Store cells in original packaging until use
• Use a proper battery holder (Keystone 142 or equivalent) — do NOT solder directly to bare cells unless they have factory-installed solder tabs (e.g., LSH14-FT variant)
• Work in a ventilated area
• Wear safety glasses when handling cells
• Use a multimeter to verify polarity before connecting circuit
• Treat the cell as live the moment the pull-tab is removed — it is

• Short the terminals (even briefly)
• Solder directly to a bare cell terminal — heat damages the seal and can cause venting
• Charge a Li-SOCl₂ cell — they are PRIMARY (non-rechargeable) and will vent or explode if charged
• Puncture, crush, or disassemble cells
• Incinerate cells
• Mix old and new cells, or different chemistries
• Store loose cells in pockets, drawers, or anywhere they can short against keys, coins, or other metal
• Ship cells by air without proper UN 3090 packaging (see Transport)

Li-SOCl₂ cells exhibit "voltage delay" after long storage. When first loaded, the cell voltage may dip briefly (100ms to several seconds) before recovering. This is normal. The supercap on the input of the boost converter handles this — do not omit it.

A cell that has been stored for 5+ years may show pronounced voltage delay. The Lazarus circuit is designed to ride through this. If you bench-test a freshly-pulled cell after long storage, expect a 0.5-1.0V dip for the first half-second.

The enclosure has a slot vent on the side wall opposite the LED. This is not optional. Li-SOCl₂ cells have a built-in pressure relief vent in the can. If a cell fails (mechanical damage, short, etc.), it will vent gas. A sealed enclosure with a venting cell becomes a pressurized container.

The vent slot allows pressure to escape. For splash/dust resistance, cover the vent internally with a PTFE membrane patch (Gore PMF1010 or similar). PTFE is gas-permeable but liquid-proof.

Single Li-SOCl₂ cells in personal quantities (≤2 cells, ≤5g lithium per cell) are generally allowed in carry-on baggage under IATA/DOT rules, but:

• Always check current regulations before flying — rules change
• Cells must be protected against short-circuit (original packaging or individual plastic bags)
• An assembled Lazarus unit with the pull-tab intact is "equipment containing a battery" — usually fine in carry-on, but declare if asked
• An activated Lazarus is "used equipment containing a battery" — same rules, but inspect for damage first

Do not ship loose Li-SOCl₂ cells by air without UN 3090 hazmat packaging and proper documentation. This requires hazmat certification.

Ground shipment within the US for personal quantities is generally unrestricted but consult USPS/UPS/FedEx current rules before shipping.

A used or expired Lazarus unit contains a partially or fully discharged Li-SOCl₂ cell. Do not throw in regular trash.

• Take to a household hazardous waste facility
• Or a battery recycling drop-off (Call2Recycle, Home Depot, Lowe's, Best Buy — call ahead to confirm Li-SOCl₂ is accepted, as some recyclers only take Li-ion)
• A fully discharged Li-SOCl₂ cell is much less reactive than a fresh one but still contains lithium and should be recycled, not landfilled

Replace the unit every 5 years regardless of apparent condition.

• Cell rated 10+ year shelf life, derated to 5 years for hot-vehicle storage
• Write manufacture date on the side label at assembly
• Set a calendar reminder
• Inspect annually for: enclosure cracking, label legibility, cap looseness

If you ever observe:

• Bulging or deformation of the enclosure
• Discoloration around the vent
• Liquid residue
• Strong sulfur or chemical odor

…dispose of the unit immediately following the Disposal procedure above.

If you build a Lazarus unit and encounter any safety issue (cell venting, enclosure failure, unexpected behavior), please file a GitHub issue with details. Include:

• Manufacture date
• Storage location (vehicle make/model, glovebox vs trunk vs etc.)
• Ambient temperature range observed
• Cell brand and date code
• Observed failure mode

Public failure reports help everyone build safer units.