Battery fundamentals

Both are flat blade terminals on small VRLA batteries. F2 blades are wider than F1. They are not interchangeable without adapters, and getting it wrong is a common ordering error on replacement batteries. Larger stationary and front terminal batteries use threaded inserts (commonly M6 or M8) or bolt-through terminals instead.

Engraved or printed on the top of the case. Record it at installation. It is what a warranty claim is assessed against, and it is the only way to establish true age on a bank that has been partially replaced over the years. Photograph the labels at commissioning; it takes five minutes and saves an argument later.

Both are VRLA, valve regulated lead acid, meaning sealed valves and immobilised electrolyte with internal gas recombination, so they do not require watering and can be installed in a wider range of locations than a flooded cell.

The difference is how the electrolyte is immobilised:

AGM uses an absorbent glass mat separator holding the electrolyte in suspension. It has lower internal impedance, which makes it better at delivering high current for short periods, the classic UPS duty, where a battery sits on float for months and then has to deliver a heavy load for minutes.

Gel uses a polyethylene separator with a thixotropic gel electrolyte. It has higher tolerance of deep discharge and better cycle life, and typically performs better at sustained elevated temperature. That makes it the stronger choice for cyclic duty and for hot, uncontrolled environments, solar and off-grid applications, remote sites, and locations that are repeatedly discharged deeply rather than occasionally.

The rule of thumb: AGM for standby with high current draw, gel for cycling and for heat. Valen’s front terminal ranges span both:

Industrial batteries fall into two families. Lead-acid divides into flooded (wet cell), VRLA, valve regulated, sealed, with immobilised electrolyte, available as AGM or gel, and OPzV tubular gel. Lithium in industrial standby is almost entirely LiFePO₄ (lithium iron phosphate), chosen over the NMC and NCA chemistries used in vehicles for its thermal stability. Valen supplies AGM, gel, lead carbon and LiFePO₄; not flooded automotive types.

VRLA means the cell is sealed with a pressure relief valve and the electrolyte is immobilised, in a glass mat separator (AGM) or a thixotropic gel. Gas generated on charge recombines internally rather than escaping, so the battery needs no watering and can be installed in orientations and locations a flooded cell cannot. Recombination is not perfect: under over-charge or high temperature the valves vent hydrogen, which is why ventilation is still required.

A battery designed to release its charge over a long period and to tolerate being repeatedly discharged to a significant depth. Thicker plates and different separator construction than a starting battery, which is built for a very high current draw over seconds. A deep cycle battery in a starting application underperforms; a starting battery in a cyclic application fails quickly.

Standby (float) use: the battery sits fully charged on a charger and discharges rarely, UPS, telecom reserve, substation tripping supply. Life is governed by calendar ageing, temperature and float voltage. Cycle use: the battery is discharged and recharged regularly, solar, off-grid, SAPS. Life is governed by cycle count and depth of discharge. The same battery is not optimal for both, and the most common specification error in this market is buying a standby product for a cycling duty.

Front terminal Q7.14. [what does C10 C20 mean battery]

12 V is the nominal voltage; 7 Ah is the capacity measured over a 20-hour discharge. Discharged at 350 mA for 20 hours the battery delivers its rated capacity.It does not mean you can draw 7 A for one hour, the one-hour rate for that battery is closer to 3.6 A, because faster discharge extracts less total energy.

[why does battery capacity change with discharge rate] Two reasons. Discharge rate: slower discharge extracts more energy, so C₁₀₀ capacity exceeds C₂₀ exceeds C₁₀. And cut-off voltage: the same battery quoted to 1.75 V per cell and to 1.80 V per cell shows different capacities. Compare batteries only at the same rate and the same cut-off. Example: a cell rated 1000 Ah at C₁₀ may be rated 1200 Ah at C₁₀₀.

Watts = amps × volts. Watt-hours = volts × amp-hours. A 12 V 9 Ah battery stores 108 Wh. A 24 V 500 Ah bank stores 12,000 Wh, or 12 kWh. A 48 V (51.2 V nominal) 100 Ah lithium module stores approximately 5.1 kWh. UPS loads are usually specified in watts or kVA, so converting the load to watt-hours before sizing is the necessary first step.

Grid supply is alternating current, the direction of flow reverses cyclically, at 50 Hz in Australia. Batteries and solar panels produce direct current, flowing in one direction. Most industrial control, communications and signalling equipment runs natively on DC (12, 24, 48, 50, 110 or 125 V), which is why those sites use DC power systems rather than AC with local rectification.