Battery (lead-acid / NiMH)
Battery
The old reliables of rechargeable storage. Lead-acid: cheap, heavy, delivers huge cranking currents, hates deep discharge. NiMH: benign chemistry in AA form, tolerant of abuse, self-discharges faster.
Schematic symbol
Battery / cell
How battery (lead-acid / nimh) appears in a circuit diagram.
Types & variants
Key specs
Voltage
VLead-acid: 2 V/cell (12 V = 6 cells); NiMH: 1.2 V/cell.
Capacity
AhAt a stated discharge rate — capacity shrinks at high current (Peukert).
Cycle life
cyclesStrongly depends on depth of discharge; shallow cycles = long life.
Charge voltage/current
V / ASLA: 13.6–13.8 V float, 14.4 V absorb; NiMH: −ΔV terminated.
Markings
Voltage, Ah and terminal polarity moulded on the case; date codes matter — they age on the shelf.
Standard values
12 V 7 Ah SLA (the UPS/alarm brick), 12 V 35–200 Ah deep-cycle, AA NiMH 1900–2500 mAh.
How to choose
SLA for cheap standby power and inverters; deep-cycle (not car) batteries for solar; low-self-discharge NiMH for anything that took alkaline AAs.
Pinout & package
SLA: F1/F2 spade terminals or bolt posts. Observe polarity — reversed connection is violent.
Example circuits
- 12 V 7 Ah + charger board as a mini UPS
- Solar setup: panel + charge controller + deep-cycle battery
- 4×NiMH pack replacing 6 V of alkalines
Common failures
Sulfation from sitting discharged (the #1 killer), dried-out cells in old SLAs, one weak cell dragging a pack down; NiMH: crystalline memory-ish capacity loss and vented cells from overcharge.
How to test
Rested open-circuit voltage: 12.7 V = full SLA, 12.0 V ≈ 25%, below 11.8 V = deeply discharged. Real health needs a load test — voltage collapsing under load means high internal resistance.
Substitutes
LiFePO₄ drop-in (with its own BMS) replaces SLA at a quarter of the weight for 4× the price; NiMH and alkaline interchange in most devices despite the 1.2 vs 1.5 V difference.