Battery Charge Algorithms

Lead-acid

Bulk

Constant current (C/5 to C/10) until ~14.4 V (12 V pack)

Absorption

Constant voltage at 14.4 V until current tapers to C/50

Float

13.6 – 13.8 V continuous maintenance

Equalize

Periodic 15.5 V burst for flooded cells (not AGM/gel)

NiMH / NiCd

Slow

C/10 for 14–16 h — no termination needed

Fast

0.5C – 1C with termination: −ΔV (NiCd ~5 mV/cell drop) or +ΔT/Δt (NiMH temp rise)

Trickle

C/50 – C/30 for maintenance

Li-ion / LiPo (CC/CV)

Phase 1 (CC)

Constant current at 0.5C – 1C until cell hits 4.2 V (or 3.65 V for LiFePO₄)

Phase 2 (CV)

Hold voltage, current drops. Terminate when current < C/20 – C/10

Precharge

If cell < 2.8 V, trickle at C/10 until normal range

Never

Exceed 4.25 V/cell. Disconnect if cell < 2.5 V. Do not charge below 0 °C (plating).

Modern fast-charge

• Multi-step CC: step current down as voltage rises — faster than CC/CV alone.
• Pulse charging: brief rest intervals reduce internal heating; disputed benefit.
• USB PD / PPS: phone and supply negotiate fine-grained voltage matching battery, skipping buck stage.
• Cell balancing (BMS): bleeds off hot cells or shunts charge — essential in multi-cell Li packs.