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The 5 stages of finance grief
Denial that manual reconciliation is acceptable
Anger over the lack of spend visibility
Bargaining with colleagues to submit expense receipts
Depression for the late nights closing the books
Accepting Ramp to skip the first 4
AS 4086.1 AS 4509.2
The Fundamental Battery Trade-Off
Every battery chemistry exhibits an inverse relationship between depth of discharge (DoD) and cycle life. Use more of the battery's capacity each cycle, and the battery wears out faster. This is not a defect — it is an electrochemical fundamental of all rechargeable batteries. AS 4509.2 explicitly addresses this in its battery sizing methodology.
DoD vs Cycle Life — Typical Values
Chemistry | DoD 30% | DoD 50% | DoD 80% | DoD 100% |
|---|---|---|---|---|
Flooded lead-acid | 1,500–2,000 cycles | 700–1,000 cycles | 300–500 cycles | 100–200 cycles |
AGM lead-acid | 1,000–1,500 cycles | 500–800 cycles | 200–400 cycles | 50–100 cycles |
LiFePO4 | 6,000–8,000 cycles | 4,000–6,000 cycles | 2,000–4,000 cycles | 1,000–2,000 cycles |
Economic Optimisation of DoD
The optimal DoD is the one that minimises the cost per kWh delivered over the battery's lifetime:
Cost/kWh = Battery cost ($) / (Cycles × Capacity × DoD × Efficiency)
For a 200 Ah / 48 V (9.6 kWh) LiFePO4 battery costing $4,000:
At 50% DoD: Cost/kWh = $4,000 / (5,000 × 9.6 × 0.50 × 0.97) = $0.17/kWh
At 80% DoD: Cost/kWh = $4,000 / (3,000 × 9.6 × 0.80 × 0.97) = $0.18/kWh
The costs are similar in this example, which is why LiFePO4 manufacturers typically recommend 80% DoD as the design point — you get more energy per charge cycle without meaningfully increasing the per-kWh cost.
Engr. Jason Morales — Founder, SolarEnergyPH
