On Fri, 16 Dec 2005 02:17:54 +1300, you wrote:

>I have a volume application that requires a battery.
>Best choice seems to be "sealed lead acid" (SLA) for reasons listed
>below. Suggested alternatives welcome.
>
>
>Requirement:
>
>Rechargeable battery.
>Good shelf life under self discharge.
>Lowest practical cost.
>OK recharge rate (faster the better).
>Reasonable capacity - say 1 to 2 AH OK.
>Battery life needs not be optimum but should be reasonable. ie some
>violation of best practice float etc voltages and charge currents is
>OK as long as battery life of say 3+ years is achievable.  Much of
>this equipment gets very little use but some is used extensively. A
>mains supply is a possible option in some cases but cannot be relied
>on. Mass and volume energy densities are not important.
>
>Alternator output is rectified to a smoothed DC rail and may reach 120
>VDC plus in some cases. For reasons not covered here this is to be
>converted to battery charging and equipment supply voltage by a linear
>regulator so dissipation is up to about 30 Watt worst case for short
>periods. This can be handled OK.
>

The big problem with SLA is that if it is allowed to discharge and stay flat for long periods, the
battery is then useless. If the nature of the product is such that it may be left unused for over a
month, I would at the very least put in an undervoltage cutout arrangement to prevent deep
discharge.  

I think Li-Ion is the only thing that is going to do the job really well. Look at a standard format
used by digital cameras or camcorders, as these are multi-sourced and pretty cheap, but keep an eye
on product quality as Bad Things can happen when Li-Ions attack..!

 
 

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