Battery Types
Battery Construction - Anodes (negative) and cathodes (positive) in cells wired in series, resting in an electrolyte
Positive and negative terminals - energy flows in either direction depending if charging or discharging
Anode, cathode and electrolyte chemistry vary
Efficiency = Power out / Power in
Lead acid - 80-85% ; Li-ion - 90-95%
Depth of Discharge vs State of Charge - DoD and SoC are inverse measurements of the remaining energy in a battery relative to its capacity
Capacity - Lead Acid depends on rate of discharge, the “C/h” rate
Available Power (for charging and more importantly discharging) - depends on internal resistance of battery.
Lead acid - discharge is usually rated at C/20, charge at C/3-C/7
Eg. A 1050 Ah with C/5 charging will absorb 210 Ah per hour
Li-ion - charge rate is usualy C/1 - C/0.5
Eg. 1050 Ah with C/0.5 will absorb 1050 Ah in 0.5 hours
Power Rating or “Max Power” - Product of max discharge amps and system voltage
Lead Acid Batteries
Flooded - Each cell is 2-volts * nominal *, least expensive
One vent cap per cell, eg. 3 vent caps = 6VDC
Cells connected in series with terminals on opposite ends
Sizing - Reverse correlation between system capacity and ideal individual battery voltage
Chemistry - Full discharge damages battery with sulfation and allows it to freeze * DO NOT PUT BATTERIES IN AREA THAT FREEZES *
Flooded require distilled water, but can overcharge harder to desulfate the electrodes! Good for standalone
For example see TROJAN T105-RE Deep-Cycle Battery
Valve-regulated - AKA Absorbed Glass Mat (AGM) or Gel, are more expensive
No removable vent caps, just valves to regulate pressure
Better for back-up systems / less maintenance; shorter lifetime (less cycles)
Sensitive to overcharging and high temperatures
No-spill, some can be installed on side
AGM - Electrolyte absorbed into a fiberglass mat
Very common, side-install into rack with integrated busbars for industrial applications.
For example see Trojan Solar AGM 12V 205AH at 20 HR Deep Cycle Battery
Gel - Can be more expensive, better for deep discharges
Capacity - Measured in Amp-hours (Ah) or watt-hours (Wh)
Influenced by temp and discharge rate (C/h)
Voltage - Affected by state, always measure at resting
Wondering about Lithium ion batteries? Since they are much more sensitive than lead-acid, that is a good place to start the conversation about charge controllers. Read on to Charge Controllers and Lithium Batteries !
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