Batteries for a layman

[1eyedjack]

Now, now, hold fire on the jargon, please, I know NOTHING.

 

But I have a gadget powered by batteries (it is a timer for an automatic garden irrigation system). The instruction manual enjoins me to use alkaline, non-rechargeable batteries. I am abjured from using any other sort on pain of .... well, pain.

 

The manufacturer of the gadget has no financial stake in whatever battery supplier I choose, so I reluctantly conclude that that the advice is at face value.

 

But to me, a volt is a volt is a volt. Just as a dollar, pound or penny loses the identity of its source once it is in my wallet, I do not expect an item of electronic equipment to be overly "concerned" whether an ampere here or there comes from an alkaline battery, NI-Mh, Ni-Cad, lithium-ion, polymer or what the heck. If the potential diffence between plus and minus fits the spec, then great. Same goes for whether the battery has been run down, charged up, run down again however many times.

 

For sure, I can well believe that one battery may maintain its charge longer than another, or that its long term life may be limited by recharge frequency etc. But I can cater for that by replacing the batteries or recharging at an appropriate frequency, and that is not the point being expressed in the manual.

 

So, what's that all about?

 

Thanks for any insight

[YT2095]

there`s 2 points really, one there is a Voltage discrepancy of .25 volts between each unit used, Alkaline bats are 1.5v each, NiCad are 1.25v, so in a multiple arrangement you can be down a whole volt in 4 cells!

 

also Ni-Cads have a lower internal resistance allowing a huge amount of current to be released on a short circuit condition (dangerous for some applications).

 

I can`t comment on your particular application or any of the product specs, but those 2 reasons outlined May have some bearing on it`s functionality or longevity.

[John Cuthber]

It may be due to the fact the some rechargeable batteries go flat relatively quickly, even if they are not doing much. That's not good for a timer.

[Human oxide]

don't lithium batteries discharge relatively quickly also ?

[jrayj]

Yes lithium batteries do discharge quickly.

[John Cuthber]

230,000 hits on Google for "10 year" lithium suggests that not all Li batteries discharge quickly.

[Flashman]

Lithium have long shelf life but deteriorate rapidly when asked to deliver high currents. Hence they are better in very low current draw applications. If they merely run the timer then they'd work very well, if they need to switch a relay, then they might not be so good. Alkaline last quite a long time even for high current draws if used for brief periods and allowed recovery time. Therefore I'd imagine that with periods of very low current draw interspersed with holding a relay or solenoid open would make alkaline close to ideal for the application.

[YT2095]

I use Lithium batts in my dSLR, it draws 7.5w from the 6 volt pack, that`s 1.25 amps.

Alkaline, although they will work in an emergency, don`t last anywhere Near as long as the Lithium cells.

the same applies to the flashgun, the Li cells give a faster cycle rate and last much longer too.

[Flashman]

Ah yes, I was thinking about the older lithium manganese dioxide cells, (Typically button type, N, half AA and other strange sizes) the newer lithium iron (not to be confused with lithium ion) cells are much better in high discharge, have long storage life but have no advantage for low discharge use (Energiser Lithium and competitive products are of this type)

Edited November 7, 2008 by Flashman