Renvu

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