Battery Drain Calculator

Peukert-corrected · AGM/flooded/LiFePO4

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Battery type

Engine state

70Ah

Amp-hours at the 20-hour rate

30300
130A

Actual output now: 52 A

30A

Peak current when compressor runs

580
40%

% of time the compressor is actively running

0100
10A

Stereo, lights, fans already running

050

Alternator keeps up

∞

Alternator delivers 52 A, which covers the 22 A average load. You can run this setup indefinitely at the current engine state.

Load vs. alternator

Total load22 A
Alternator output52 A

Peukert check

Rated capacity (20-hr)
70 Ah
Peukert-adjusted capacity
48.5 Ah
Usable before damage
38.8 Ah (80% DoD)
Average total load
22 A

Lead-acid batteries deliver less than their rated capacity at high discharge rates — a 100 Ah battery rated at the 20-hour rate only gives ~65 Ah when pulling 30 A continuously. We apply the Peukert equation (t = H × (C / I·H)^k) with k = 1.2 for AGM (XS / Optima / Odyssey). Lithium's flat discharge curve means Peukert barely matters (k ≈ 1.05) — one reason LiFePO4 drop-ins punch above their rated Ah.