Batteries for Audio: Comparison of Widely Available Battery Technologies used in Audio Applications

- such as power supplies for audio amplifiers

Property

Battery Technology

(Shaded if Impacts Audio Performance)

Significance

AGM*

Nickel / Metal Hydride

Lithium Ion

Lithium Metal

Alkaline (AAA, AA, C or D cells)

Alkaline (or Lithium) 9V

Rechargeability

Longevity and User Convenience
 > Yes Yes Yes No (See Note 1) No (See Note 2) No

Easy to Obtain

User Convenience
 >

Yes

Home Centers, Internet: Industrial Supply (e.g., McMaster-Carr), Electronic Supply (e.g., Digi-Key)

Yes, but depends on design (sometimes limited sources) Depends on design (sometimes only single source for proprietary designs) Extremely Easy Extremely Easy Extremely Easy

Life Cycle Cost

Lower is Better
 > Low to Medium Low to Medium Medium Medium to High (replaced after discharge) Medium (replaced after discharge) Medium (replaced after discharge)

Life:

Longer is Better
 >

Long to Very Long

up to 20 years

Medium to Long (for consumer grades)

2 to 3 years

Long

3 to 5 years

Single Use Single Use Single Use

Single Cell Voltage

Higher is Better (Fewer Cells in Series)
 > 2.0 to 2.1 Volts 1.2 Volts 3.6 Volts 3 Volts 1.5 Volts 1.5 (or 3) Volts

End of Discharge Voltage, per cell

Higher is Better
 > 1.8 Volts 1.0 to 1.1 Volts 3.2 Volts 2.5 to 2.7 Volts 0.8 Volts 0.8 Volts

End of Discharge Voltage as Percentage of Initial Cell Voltage

Higher is Better (indicates stability of power supply voltage)
 > more than 80 % approx. 90 % approx. 90 % approx. 90 % less than 60 % less than 60 %

Electrical Impedance

Lower is Better

Audio: Important for Electromagnetic Noise Immunity; Greater Transient Current Capability; High Discharge Rate Capability
 > Extremely Low Extremely Low Medium (sometimes deliberately limited for safety reasons) Low to Medium (sometimes deliberately limited for safety reasons) High High to Very High

Change in Cell Impedance at End of Discharge

Smaller is Better (for same reasons given for impedance, above)
 > Small Small to Medium Medium Small to Medium Very Large Very Large

Series Cell Connections

Internal are Best

Audio Microphonics / Noise: Low Integrity of Friction-type, Mechanical Contact Connections (See Note 3) plus Radio Frequency (RF) interference from contact contamination (rectification of RF electromagnetic pickup)
 >

Internal, low impedance, high-reliability intercell connections, 3 or 6 cells (for 6 or 12V)

High Integrity battery external terminal connections (lugs)

Internal; 5 cells (for 6V) hard-wired or spot-welded inside battery pack (see Note 7)

High Integrity battery external terminal connections (lugs or flying leads)

Internal; cells hard-wired inside battery pack

Battery external terminal connections of varying types, sometimes friction-type

External Intercell Connections required above 3 V

Battery external terminal connections of varying types, sometimes friction-type

External Intercell Connections required above 1.5 V

Always friction-type external terminal connections, cannot solder

Internal Connections of 6 (or 3) cells

High Integrity battery external terminal connections (snap on)

Battery Power Delivery Capability for a given Physical Size or Volume (watts of power per unit volume)

Higher is Better (See Note 4)

Audio: Important for Electromagnetic Noise Immunity (a Large, High Impedance Battery acts as an Antenna)
 > Medium to High Medium to High High to Very High High to Very High Low (See Note 5) Very Low (See Note 5)

Battery Energy Density for a given Physical Size or Volume (watt-hours per unit volume)

Higher is Better (See Note 4)
 > Low Medium to High High Very High Medium (See Note 5) Medium to Low (See Note 5)

Safety in Application (see Note 6)

Higher is Better
 > High High Medium to High High High High

Complexity of Recharging Electronics

Lower is Better (Cost Impact)
 > Medium Medium to High Very High Not Applicable Not Applicable Not Applicable

"Green" Technology (Environmental Impact and Recyclability)

That Depends on You
 >

Rechargeable, Low Impact

90% of Lead Battery Waste is Recovered / Recycled; Lead Battery Recycling Channels are Well Established (automotive)

(AGM Batteries are RoHS Compliant by Exemption)

Rechargeable, Low Impact

Availability of Recycling uneven

Recycling and Nickel Recovery from Consumer Grade Cells can be Expensive

Rechargeable, Low Impact

Some Recycling

Single Use, Medium Impact

("Throw - Away," Difficult to Recycle Materials)

Usually ends up in hazardous - waste landfill

Single Use, Medium Impact

("Throw - Away," Difficult to Recycle Materials)

Usually ends up in hazardous - waste landfill

Single Use, Medium Impact

("Throw - Away," Difficult to Recycle Materials)

Usually ends up in hazardous - waste landfill

Rating for Audio Use (Favorable minus Unfavorable):

6 ******

5 *****

4 ****

4 ****

Minus 4 ****

Minus 4 ****

* AGM: Absorbent Glass Mat, sealed lead/acid

Key:

Best in Category / Favorable

Worst in Category / Unfavorable

Notes:

  • Consumer grade nickel - cadmium batteries are no longer generally available (expensive to recycle, and cadmium also has become very expensive compared to the metal hydride material that has replaced it).
  • "Lithium AA" cells are comparable to alkaline AA for audio applications.
  • Rechargeablilty, volumetric efficiency and energy density are extremely important in portable device applications, and supersede most other considerations.
  • Two 2.3 ampere-hour 6-volt AGM cells currently cost less than $50 total. For a 6 year life, this represents a life cycle cost of less than $10 per year (initial investment).
  • The cycle life for deep discharges of all of the rechargeable batteries in the table, for all practical purposes, is roughly equivalent.
  • Jargon: Primary = single-use; Secondary = rechargeable.

1. Lithium metal / vanadium pentoxide batteries are rechargeable and available in the consumer channel, but only are available in sizes too low for audio applications. The development of larger sized lithium metal secondary batteries has been the subject of decades of intensive efforts, but has been abandoned because of insurmountable safety issues.

2. "Rechargeable alkaline" cells are just a marketing gimmick that trades cycle life (number of recharges) for capacity (depth of discharge). They are only viable for shallow discharges (25 percent or less, or "periodic" use), which mean that the useful capacity is really only about 25 percent of that of a similarly-sized alkaline cell. After a deep discharge, the cycle life drops to only a few charge-discharge cycles. The audio performance is the same as conventional alkaline cells.

3. For example, when you physically strike a flashlight that contains more than one cell, what happens? What happens to an audio power supply in an acoustically live listening room environment?

4. Power delivery (watts) as a function of volume is important for audio (powerful, smaller batteries being more desirable). Power delivery as a function of weight is not important for audio (but is important for portable devices). Energy density (watt-hours) or total capacity is a convenience issue and not important for audio performance, provided that the runtime between charges (or primary battery replacement interval) is acceptable.

5. Power delivery capability (measured in watts, or volts x amperes) is not the same as energy density (watt hours, or volts x amperes x hours). The energy density of alkaline batteries is very strongly dependent on discharge rate. If rated at low (10 to 40 milliamp) discharge rates, the energy density of alkaline cells seems high. However, the power delivery capability is low, because of high internal impedance. Audio requires the battery to supply power, e.g., higher discharge rates: 80 milliamps or more of continuous current for a high performance preamplifier, in addition to transient current demands, with minimal voltage sag. This requires low cell impedance. (Using alkaline batteries in a power tool, such as a portable drill or saw, would be unthinkable; secondary / rechargeable cells are used because of their low impedance). Think of "impedance" as resistance: high impedance is the same as having a high resistance in series with the battery, undesirable for audio power supplies. This weakness can be partly overcome by using banks of electrolytic capacitors to provide a low impedance charge storage source.

6. Safety: all of the battery types listed (except for lithium ion) contain chemically corrosive (acidic or alkaline) electrolyte or plate material (lithium metal is extremely alkaline and can explode if placed in contact with liquid water, because of the released hydrogen and high temperatures generated).

  • AGM lead/acid batteries cannot release liquid electrolyte, even if the case is broken, because the electrolyte is contained in a spongelike, absorbent fiberglass-type plate separator material. This is not the same as a so-called "low maintenance" automotive type battery, which, despite sometimes being referred to as "sealed," actually are not sealed (meaning gas tight) and contain a spillable, bulk liquid electrolyte.
  • Alkaline batteries can release electrolyte if over discharged, which causes the case to swell and lose sealing.
  • Lithium ion batteries can explode if mistreated, and consequently require complicated charging electronics (expensive). This is also why they aren't being used in electric vehicles (nickel / metal hydride preferred).

7. "AA" size nickel / metal hydride individual rechargeable cells not included here; generally comparable to alkaline with the inconvenience of having to remove and recharge them periodically, unless charging circuitry is included in the hardware; plus the integrity problems of friction-type intercell connections.

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