A vaccine run has exactly one failure mode that ends the day: the cold chain breaks. Forty minutes stuck in traffic with the engine off and an undersized battery bank, and a unit’s worth of vaccine is gone — along with the trust of every patient who showed up.
Onboard medical refrigeration needs its own validated circuit, not a share of the house power. Size the inverter and battery bank for the worst case: fridge plus lighting plus diagnostics running while the engine is off, for longer than you think you’ll ever sit. Then add margin, because city traffic doesn’t care about your plan.
Temperature logging is the proof and the alarm. A continuous logger with an audible alarm tells you the moment you’re drifting out of range, while you can still do something about it — relocate stock to a backup cold-carry, cut the run short, or get power back. Logging after the fact only tells you what you lost.
This is exactly the power-and-cold-chain layer we lay out in the mobile medical clinic kits checklist, and it’s the part programs underinvest in until they lose a load. Spend on the battery bank and the logger; they’re cheaper than the vaccine they protect.
Build for the forty-minute traffic jam you haven’t hit yet, and your vaccine run survives the one you will.