wolit@rabbit.UUCP (Jan Wolitzky) (11/15/84)
Varta Batteries, Inc., Elmsford, NY 10523, makes 9.6 volt NiCad batteries and chargers for them. I tried them after discovering that the standard "9 volt" NiCads wouldn`t work for more than a few hours in my smoke alarm before setting off the "low battery" warning. Carbon-zinc cells each have a potential of 1.5 volts, so six of them go into each 9 volt battery. But NiCads only have a 1.2 volt potential, so six only make 7.2. Varta puts eight NiCad cells in their "9 volt" battery. It's been a few years, but I remember paying about $12 for the battery and charger together. (Actually, Varta's plant is in West Germany; the Elmsford address is their U.S. office.) -- Jan Wolitzky, AT&T Bell Laboratories, Murray Hill, NJ; (201) 582-2998
henry@utzoo.UUCP (Henry Spencer) (11/16/84)
> the standard "9 volt" NiCads wouldn`t work for more than a few hours > in my smoke alarm before setting off the "low battery" warning. NiCads are a poor choice for long-term low-drain applications anyway, because they do not hold charge well. This is why any NiCads you buy come with an injunction to charge before use; they will have lost their charge while sitting on the shelf. This situation is starting to change; I've seen datasheets on new NiCad designs that do hold their charge better. But NiCads are still nowhere near as good as alkalines for applications where they have to sit idle, or nearly so, for months before being called into action. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
danny@alice.UUCP ( Kahn @ Bell Communications Research, Murray Hill, NJ) (11/21/84)
The articles on rechargeable batteries (ni-cads) have been excessively negative. I have used many different brands thru dozens of cycles with no degradation. (Of course, there may be some really poor products on the market that I haven't seen.) Be sure you are following instructions when recharging. Overcharging (excessive time or current) can damage nicads; undercharging will obviously not give full performance. Where several cells in series, recharge when even only one cell discharged, otherwise weakest cells will be reverse-charged by stronger ones, with possible permanent damage. As Jan Wolitzky points out, most nicad replacements for ordinary batteries have same number of CELLS, thus lower open-circuit terminal voltage; in some applications, typically low-current voltage-sensitive ones, this can be a problem. However nicads have very low internal resistance compared to carbon-zinc or alkaline, so may deliver close to, as much, or more voltage PER CELL than the other types in high-current applications. Thus a cell-for-cell replacement by nicads is often appropriate in spite of the drop from 1.55 to 1.25 open-circuit voltage.