I have been monitoring battery performance for about five years, since getting a Psion 5MX. The Psion uses two AA batteries, and has a built in battery usage monitor. The Psion requires an operating voltage of at least 2.4 volts, so once the output of a cell drops below 1.2v they need replacing, although there is still power in the battery.

Most alkaline batteries give about 1600mah before the voltage drops below the critical point. Ikea/Varta manage about 1800. A few like Duracell Ultra give up to 1900mah, but this is only a difference of about 10% between the best and worse performers. The difference in price however ranges from 19p each for Ikea batteries, to £1.12 for Duracell Ultra (Dixons) - Prices as at 27/11/04. As with all things, shop around - and remember that the larger packs are often much cheaper per battery.

There are 7 basic types of dry-cell battery available in the popular sizes, and these can be split into two groups:

Non-Rechargeable

Zinc Carbon - 1.5volt

This is the standard cheap type of battery, BUT a Zinc Carbon battery from a leading supplier such as Ever_Ready/Energizer may well be more expensive than a non-branded alkaline battery. They are prone to leaking, and not therefore not suitable for prolonged use.

Zinc Chloride - 1.5volt

Similar to Zinc Carbon, but less prone to leakage. Otherwise, the comments above apply.

For more information on both the above, see Martin Hilliers Techweb.

Alkaline - 1.5 volt

The market leader is Duracell. Their adverts claim is that they last up to 6 times longer than ordinary Zinc Carbon Batteries. However, this is true for pretty well ANY alkaline battery. My own tests have shown that Standard Duracell batteries are NOT the longest lasting alkaline battery, at least as far as Psion PDA's are concerned. They are however, one of the most expensive. I have not tested Duracell Ultra.

The other leading manufacture in the UK is Ever Ready/Energizer - Their prices are not much better than Duracell. I suspect the inflated prices are due to their advertising budgets!!!

Lithium - 1.5 volt

These are not rechargeable - Don't even try!!.

They are more expensive, but with up to twice the output of standard alkalines. Price from 7dayshop.com for 4 batteries is 5.75 UKP + P&P. (99 pence per order)  (7dayshop claim up to 5 times the life of standard alkalines, but other opinions are not so optimistic) They weigh considerably less than Alkaline batteries. For example, I have a Techass Eternalight Elite X-ray torch which will float when fitted with Lithium batteries, but not Alkalines.

The reactive nature of Lithium to air give these cells their high shelf life, which is measured in decades. They can withstand high temperature variations and are virtually leak proof.

They are ideal for low drain applications such as smoke alarms and data retention. The high price is justified with a very long life.

Brand	mAh / Pair	Pack Size	Pack Price (UKP)	Price/Battery UKP
Standard Duracell	1600	4	2.20	1.00
Ikea (Actually Varta batteries, Branded for Ikea)	1600	10	1.90	0.19
Sony Stamina	1350			0.72
Lidl (Daimon)	1300	4	2.99	0.75
Ever Ready Energizer

It is possible to buy transformers which will recharge alkaline batteries. Innovations Catalogue in the UK market one. See http://www.innovations.co.uk/, but at 35.00 UKP, it is not cheap.

However, note:-

1. Most normal alkaline batteries have a gas vent that will open if the battery is charged. This is a one-time valve, and does not reseal. This means that the battery is then liable to leak.
2. SOME batteries do not have any vent, and MAY explode if charging is attempted.
3. Some batteries apparently cannot be re-charged - I don't know why - I suppose that They may have circuitry built in to prevent it.

Rechargeable

NiCd - 1.2 volt

The most common rechargeable batteries are Nickel Cadmium. NiCad Batteries only give 1.2v to start with, and are unsuitable for use in a Psion. The only time I tried them, they gave me about an hour of usage, and then the voltage dropped so quickly, that the Compact flash (Drive D:) was corrupted while data was being written, so I had to re-format it and then restore the data from backup. They are however very suitable for use in Toys.

NiCd batteries can normally be recharged between 500 & 1000 times, but if recharged before they are completely discharged can develop a "Memory Effect". In fact, a layer of crystals develops across the cell, and prevents the full capacity of the cell from being used. There are some chargers that claim to restore NiCd batteries, but I have no experience of them.

NiMH - 1.2 volt

From what I read, they seem to give about the same power output as standard Alkaline batteries, but are rechargeable. Screwfix sell 4 * AA batteries for 3.99 UKP + P&P. Rayovac's charger for their rechargeable alkaline batteries can also be used to charge NiMH and NiCd batteries. In fact, most chargers handle NiMH and NiCd batteries.

The only problem is that, unfortunately, many items are still not designed to use the lower voltage of rechargeable batteries.

Once charged and stored, NiMH batteries discharge in around 60-90 days.

Rechargeable Alkaline - 1.5 volt

Genuine Rechargeable Alkaline batteries are available, and as with all alkaline cells, have an output voltage of 1.5v. The only ones I have used are made by Rayovac, and their only high street stockist was Focus Do-It-All, but other makes are available on the web. For example see www.budgetbatteries.com

A 4 x AA charger with 2 AA cells is around 10.00 UKP, and 4 AA cells are about 5.00 UKP. Output of two cells is about 500 Mah, which is considereably less than standard Alkaline batteries, but they are still cheaper to use, and better for the environment. They can be recharged up to 50 times, and since a pack of Duracell Batteries is also around 5.00 UKP they offer very good value for money.

HOWEVER, they do not give the same output as a standard alkaline. When I was using them in my Psion 5mx, I used to get around 700 mAh from a pair before they needed recharging, as opposed to around 1200-1500mAh from normal alkalines,  BUT at least they CAN be recharged.

CONCLUSIONS AND FINAL OBSERVATIONS.

Use the cheapest Alkaline battery you can lay your hands on, not the most expensive. 

Virtually ANY alkaline battery is better value than Duracell.

See this comment in the on-line price catalogue at www.7dayshop.com

Why Are You Even Thinking of Buying Duracell Batteries…?
” Make the Switch to Panasonic PowerMax3 Today ~ We sell loads more Panasonic batteries than Duracell to our customers and the prices are much better too ! “

Although my own observations are based on AA batteries, there is no reason to suppose that comparing price versus performance of any other size of battery will give a wildly differing result.

I really don't understand why Rechargeable Alkaline batteries are so difficult to get hold of. The technology is much better than Ni-Cad, and with their full 1.5 volt output, they will work in units requiring a higher voltage.

 

For more information, also see:-

Kevin Millican's Web site about batteries. However, Kevin has not updated his notes for quite a while now.
http://www.m-j-h.pwp.blueyonder.co.uk/hiltec/elec/battery.html
http://www.battery-technology.co.uk
http://www.greenbatteries.com/
DAFT UK Web Site
Digital Imaging Web Site

Test results by Tantronics.co.uk - (This page is no longer available on-line)

Price and Performance Comparisons for Leading Brand Batteries We (Tantronics) have conducted tests on leading brand batteries to investigate their "Real Life" performance when used in the Psion Series 5 and Series 5mx. Several sets of batteries were used to give reasonable results based on average consumption's of between 70mAh and 100mAh. We did however find a number of "Bad" (lower than normal capacity) cells from all the brands tested. Both machines were left on permanently during these experiments to ensure the reports were consistent It should be noted that the achieved capacity is as reported by the Psion "Battery Information" screen. This is not a measured figure, but appears to be calculated by the internal software, hence the difference between the two machines. Of course the cynical among you may think that because we sell the GP alkalines, the results are biased in their favour. You will undoubtedly have done your own comparisons too, but what we have demonstrated here is that there is a relatively small capacity difference between brands. With that in mind, there seems little point in paying for expensive makes, just because they are well known, but that is your choice. RED - Best Figure    BLUE - 2nd Best Figure Psion Series 5   Duracell Ultra GP Super Alkaline Duracell Panasonic Power Alkaline Sony Alkaline Woolworth's Alkaline Typical Cost £1.94 £0.75 £1.46 £1.35 £1.50 £1.25 Reported Capacity 2122mAh 100% 2048mAh 96.5% 2010mAh 94.7% 1975 mAh 93% 1899mAh 89.5% 1819mAh 85.7% Cost Per Hour @ 70mA £0.064 £0.026 £0.051 £0.048 £0.055 £0.048 Psion Series 5mx   Duracell GP Super Alkaline Panasonic Power Alkaline Duracell Ultra Sony Alkaline Woolworth's Alkaline Typical Cost £1.46 £0.75 £1.35 £1.94 £1.50 £1.25 Reported Capacity 1803mAh 100% 1781mAh 98.8% 1748mAh 96.9% 1735mAh 96.2% 1726mAh 95.7% 1563 mAh 86.7% Cost Per Hour @ 100mA £0.081 £0.042 £0.077 £0.112 £0.087 £0.08

For cheaper battery Supplies:-

Batteries Online
Battery Masters
Budget Batteries
Power Store Direct
7 Day Shop

 

(Please note that I have absolutely no financial interest in any of the companies mentioned on this page)

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