Aqualab: Research: Which Kind of Battery?

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Research Topic: Which Battery Will Do?

Last updated:

Overview & Terms
8 March 2012

Single Use
7 January 2016

Rechargeable
10 November 2019

Battery Analyser
23 April 2021

Battery/Charger Shopping
24 April 2021

Original article by Ian Mander, 22 July 2002

Single Use Test
6 November 2007

Rechargeable Test
21 September 2023

Test Procedure
4 June 2011

Button and Coin Cell Shopping
31 July 2021

More Info & Links
29 February 2012

LSD Shootout
7 January 2016

When Battery Testing
Goes Bad –
Consumer Magazine
4 February 2025

Battery Holder Shopping
28 July 2022

On this page: Rechargeable Battery Types | Miscellanous notes | Treatment of NiCd and NiMH

Rechargeable (Secondary) Battery Types

If you use NiCd or NiMH cells please read the treatment of NiCd and NiMH rechargeables section below before moving on from this page.

Battery type (Rechargeable)	Pros	Cons
Lead acid 30-50 Wh/kg 85-90 Wh/L	Extremely high current output - low internal resistance - very high conversion efficiency (80-85%). No voltage depression ("memory" effect). Can be tailored for particular use (eg, deep cycle). Low cost. Low to medium self discharge (8-40% per month).	Dangerous chemicals used (lead, sulfuric acid). Heavy. Low storage density - "The energy a lead-acid battery stores per [kilogram] of battery is lower than just about any technology short of a potato wired with zinc plates." Reduced capacity with increased temperature (50% with each 8°C). Reduced capacity under heavy loads (Peukert Effect) - worse than sealed lead acid. Cannot be stored flat.
Sealed lead acid (gel cell or absorbed glass mat) 30-50 Wh/kg 85-90 Wh/L	Sealed, and so much safer than standard lead acid. Extremely high current output - low internal resistance - extremely high conversion efficiency (gel 85-90%, AGM 95%). No voltage depression ("memory" effect). Low cost. Low self discharge (2-10% per month).	Does not like deep discharging. Can (permanently) die suddenly. Cannot be fully charged. Heavy. Low storage density. Reduced capacity with increased temperature (50% with each 8°C). Reduced capacity under heavy loads (Peukert Effect), although not as bad as lead acid. Cannot be stored flat.
Rechargeable alkaline 80 Wh/kg (initial)	Batteries and chargers are less expensive than other types. No cadmium (more environmentally friendly than NiCd). Very low self discharge	Require a special sort of charger. Cannot be recharged as many times as other types (25 to 100 times). Cannot be fast-charged. Reduced capacity under heavy loads (Peukert Effect). Can have a reduced capacity after several charge/discharge cycles.
NiCd rechargeable (nickel cadmium) 40-80 Wh/kg 100-150 Wh/L	Extremely high current output - low internal resistance - high conversion efficiency (65%). Not much capacity loss under heavy loads (little to no Peukert Effect). Very level output voltage curve, holding very steady at 1.2V until almost flat. Can be recharged many times (500-1000) if maintained properly. Copes very well with abuse such as heavy loads, deep discharge, etc, if maintained properly. Can be stored in any state of charge.	Cadmium is bad for the environment. Cells exhibit voltage depression ("memory" effect) if recharged from a less than completely flat state (ie, they go flat before they should). Must not be over discharged. Reduced capacity with increased temperature (20% with each 8°C). Careful handling required because of high current output - don't carry in your pocket, especially with a set of car keys.
NiZn rechargeable (nickel zinc) 60 Wh/kg 100-170 Wh/L	Similar to NiCd but no toxic cadmium. Zinc is less expensive than cadmium. The nickel and zinc can be fully recycled. Even lower internal resistance than NiCd. Higher than normal voltage, nominal 1.6V per cell. Can be recharged many times (500-600) if treated gently. Fast recharge.	Reduced life (100-200 cycles) if heavily discharged - one manufacturer recommends using 80% discharge for longest life. Moderate self discharge rate. Careful handling required because of high current output - don't carry in your pocket, especially with a set of car keys. Charging can be tricky - for 100% charge one manufacturer suggests using 2.5C for one hour, pause 5 minutes, then use constant voltage at 2.05V. Actually first patented in 1901 but the tendency for the cathodes to break down due to dendrite formation have kept them off the shelves.
NiMH rechargeable (nickel metal hydride) 60-120 Wh/kg 220-300 Wh/L	Can give very high current output. Not much capacity loss under heavy loads (little to no Peukert Effect). Very level output voltage. Can be recharged many times (500+) if good quality and treated well. Little voltage depression ("memory" effect). No cadmium (more environmentally friendly than NiCd). Roughly 150% the gravimetric storage density (by weight) or up to 220% the volumetric storage density of NiCd. Can be stored in any state of charge.	Must not be over discharged (and prefers shallow discharges). Old technology NiMH cells have moderately high self discharge (30% per month). However, for years there have been low self discharge versions widely available. The undisputed leader is the Sanyo Eneloop (3rd generation) which claims to retain 90% of its charge after 1 year, 80% after 3 years and 70% after 5 years. Need special chargers because overcharging can damage the battery - this means an ordinary NiCd charger may damage your NiMH battery.
Lithium ion (this is a blanket term for at least 5 different chemistries*) 100-240 Wh/kg 270 Wh/L	No voltage depression ("memory" effect). Very high storage density (~200% of NiCd).	Must not be over discharged. Reduced capacity under heavy loads (Peukert Effect). Can be recharged "only" a few hundred times (less than NiCd or NiMH).
Lithium ion polymer (lithium polymer) 130-200 Wh/kg 300 Wh/L	No voltage depression ("memory" effect). Can be designed to provide extremely high discharge rates. Even higher storage density than lithium ion (up to 300% of NiCd storage density). Doesn't have to be in a cylindrical shape. Environmentally friendly.	Must not be over discharged. Reduced capacity under heavy loads (Peukert Effect). Can be recharged "only" a few hundred times (less than NiCd or NiMH).
Lithium iron phosphate (LiFePO₄) 130-170 mAh/g 90-160 Wh/kg 220 Wh/L	Higher discharge current than many other lithium batteries. Does not explode under extreme conditions like other lithium rechargeables. Much greater cycle life than other Li-ion batteries. Weigh less(?) than other Li-ion batteries. Relatively low cost. Non toxic. Does not decompose at high temperatures.	Have lower voltage (3.2V) than normal Li-ion cells so can't be charged by normal Li-ion chargers. Also have lower energy density.

* Li-ion chemistries include:

Lithium cobalt oxide, LiCoO₂ (aka ICR, LCO, Li-cobalt). Superceded by newer chemistries.
Lithium manganese oxide, LiMn₂O₄ (IMR, LMO, Li-manganese). Used for power tools.
Lithium manganese nickel cobalt oxide, LiNiMnCoO₂ (INR, NMC). Can be optimised for high power or high energy. Possibly the present leading li-ion chemistry.
Lithium nickel cobalt aluminium oxide, LiNiCoAlO₂ (NCA, NCR). High specific energy, long life span.
Lithium nickel cobalt oxide, LiNiCoO₂ (NCO).

Lower voltage Li-ion chemistries include:

Lithium iron phosphate, LiFePO₄ (LFP, Li-phosphate). Lower voltage than other chemistries.
Lithium titanate, Li₂TiO₃ (LTO). Low voltage (2.4 V). Low specific energy (between NiCd and NiMH), excellent lifespan, performance and safety.

A mix of LMO (30%, acceleration) and NMC (70%, high capacity) are used for most car batteries.

A few emerging rechargeable battery technologies are mentioned on the More Info & Links page.

Miscellaneous notes on rechargeables

I've seen one claim that it became normal to rate primary cells by their initial voltage (1.5V) and secondary cells by their average voltage (1.2V), so simply comparing the nominal voltages of the two types doesn't give an accurate idea of what voltage they'll actually be supplying when in use.

Although NiCd and NiMH are "only" a nominal 1.2V, they can actually be a whole 1.4V when fully charged and as much as 1.54V for a short while after coming off the charger. A rechargeable's voltage doesn't drop under load as much as (for example) alkaline cells' voltage does, leading to some incandescent torch bulbs burning out when run on freshly charged cells. So a 1.4+ volt rechargeable is actually more of a threat to a bulb than a brand new alkaline at almost 1.6V, since the alkaline voltage drops significantly as soon as the torch is turned on.

When you consider that half to two thirds the life of an alkaline under load may be under 1.2V anyway, and the voltage of an alkaline under load drops more than a rechargeable for the same load (because alkalines have a higher internal resistance than NiCd or NiMH), there's little point buying rechargeable alkalines to get that higher voltage - what you're actually getting is simply the more variable voltage of alkaline without the advantages of NiMH rechargeables such as a high capacity at high current.

Read Roy Lewallen's "1.2 Volt" vs. "1.5 Volt" Batteries PDF for further information.

Treatment of NiCd and NiMH rechargeables

Most rechargeable battery types do not like being deeply discharged. Over discharging them can damage the cell. Most electronic equipment won't run if the voltage drops too low so it's not a problem. If using them in a torch (for example) after the light output drops significantly, turn off the torch. As soon as the light dims noticeably the battery is discharged and needs to be changed. Don't try to milk the last little bit of power out of them because that can damage the cells. The same goes for any other electrical apparatus that doesn't switch off by itself.

The self-discharge rates of NiCd and NiMH are a little higher than lead acid and lithium. Apart from Sanyo Eneloop cells, after several months they will be completely discharged, although their shelflife can be extended by refrigerating or freezing. If freezing, do remember to thaw before using. :-) According to Duracell "Generally, long term storage of a nickel-metal hydride battery in either a charged or discharged condition has no permanent effect [sic] on capacity." Batteries that have been stored for many months can normally be restored to full capacity by several charge/discharge cycles.

Don't put fully recharged batteries back on the charger for a "top up." Overcharging can damage them. Similarly, don't leave NiMH batteries for long periods on the charger if it doesn't switch completely off. NiCd on the other hand can be continuously trickle charged, which makes it more suitable for things like solar garden lights.

Read on for test results for NiMH batteries.