description: Battery selection for cold-chain and refrigerated trucks — why reefers need a starting battery plus a separate deep-cycle auxiliary bank. type: article date_published: 2026-08-30 date_modified: 2026-08-31 faq: - q: What battery does a reefer truck need? a: A refrigerated truck needs two separate systems: a starting battery for the engine (850–1100+ CCA for a large diesel), and a deep-cycle or AGM auxiliary bank for the refrigeration unit. - q: Can I run the reefer off the starting battery? a: No. A 25 A refrigeration unit draws ~200 Ah over 8 hours and will deep-discharge a starting battery, damaging it and risking a no-start. Use a separate auxiliary bank. - q: What battery is best for the refrigeration unit? a: Deep-cycle batteries (or AGM) are best for the reefer's continuous draw — they tolerate repeated discharge to ~50% without the plate damage a starting battery suffers. - q: How do I keep the reefer from draining the starting battery? a: Use a battery isolator or DC-DC charger to separate the starting battery from the auxiliary bank, so the reefer cannot drain the starting battery. A plain isolator drops ~0.3–0.7 V; a DC-DC charger adds a proper charge profile. - q: How do I size the auxiliary bank for a reefer? a: Size it to the reefer's continuous current draw and required runtime. A 25 A unit over 8 hours needs ~200 Ah usable — ~400 Ah at the 50% depth-of-discharge limit. Confirm the unit's draw from its specification.
Batteries for Cold-Chain & Refrigerated Transport¶
TL;DR — Refrigerated trucks need two things: a starting battery with adequate CCA (850–1100+ for large diesels) for the engine, and a separate deep-cycle auxiliary bank for the reefer. A 25 A reefer running 8 hours draws ~200 Ah — which needs ~400 Ah of bank at the 50% discharge limit. Never run it off the start battery.
Key Takeaways¶
- 2 loads demand 2 battery types — a starting (SLI) battery for the 850–1100+ CCA burst and a separate deep-cycle bank for the reefer's continuous draw; one battery cannot serve both jobs.
- Never run the reefer off the starting battery — a 25 A unit draws ~200 Ah over 8 hours and deep-discharges the plates; the truck starts fine on the lot, then strands the driver mid-route after an overnight stop.
- A basic isolator only blocks reverse current, with a ~0.3–0.7 V drop — a DC-DC charger also applies a proper multi-stage charge, which a cycled deep-cycle bank needs to stay healthy over many cycles.
- For a reefer that runs 8+ hours a night, the DC-DC charger is the better investment — the isolator protects the start but does nothing for auxiliary-bank longevity, so the cheaper option is a false economy.
- Match the starting battery to your market group size (JIS N150/N200 or DIN88/DIN100) — and consider AGM for the auxiliary bank, since it tolerates cycling better than flooded.
Two Separate Loads¶
Cold-chain transport has two distinct electrical loads:
| Load | Requirement | Battery type |
|---|---|---|
| Engine starting | High CCA burst | Starting (SLI) battery |
| Refrigeration unit | Continuous power | Deep cycle / auxiliary bank |
Why Separation Matters¶
The refrigeration unit draws power continuously — often with the engine off or at idle. A starting battery is built for short, high-current bursts, not sustained deep discharge. Running a reefer off the starting battery will:
- Deep-discharge it, damaging the plates
- Shorten its service life dramatically
- Risk a no-start when the truck needs to move
The failure mode is the worst kind: the truck starts fine on the lot, then strands the driver mid-route because the reefer quietly drained the starting battery during an overnight stop.
Recommended Configuration¶
- Starting battery — dedicated to engine cranking, matched CCA to the engine and climate
- Auxiliary bank — deep cycle batteries for the refrigeration unit
- Isolation — a battery isolator or DC-DC charger prevents the reefer from draining the starting battery
Size the bank to the load, not the tray. A reefer unit drawing 25 A for 8 hours uses 200 Ah (25 × 8); because a deep-cycle battery should not be discharged below ~50%, that means a bank of ~400 Ah. Double-check the actual draw — a 40 A unit over 10 hours needs 400 Ah usable, or ~800 Ah at 50%.
Isolator vs DC-DC Charger¶
A basic battery isolator simply blocks current from flowing back from the auxiliary bank to the starting battery when the engine is off. A DC-DC charger does more: it provides a proper multi-stage charge to the auxiliary bank, which matters for deep-cycle batteries that need a controlled charge profile. For a reefer that runs for hours, a DC-DC charger is the better investment because it keeps the auxiliary bank healthy over many cycles.
Battery Selection Tips¶
- Match the starting battery's group size and CCA to the vehicle (JIS N150/N200, DIN88/DIN100)
- Size the auxiliary bank to the reefer unit's continuous draw and required runtime
- Consider AGM for the auxiliary bank — it tolerates cycling better than flooded
For how deep-cycle batteries differ from starting batteries, see starting vs deep cycle. For runtime planning, see what is reserve capacity.
References¶
- Battery Council International — deep-cycle batteries
- Battery Council International — lead battery technology
Related¶
Find the Right Battery¶
Need a specific model or datasheet? Browse the DINWEYS product range (fleet battery solutions) or contact us for a quote.