Unless low weight is the single highest priority in the design, anything other than SLA does not meet your requirements. SLA can always be recovered from a discharge state, but its remaining efficiency depends on recovery method and age. ----- Original Message ----- From: "Mike Harrison" To: "Microcontroller discussion list - Public." Sent: Thursday, December 15, 2005 8:51 AM Subject: Re: [EE] Battery choices > 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..! > > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist