Originally posted by arbutusq I read somewhere that slow chargers are easier on batteries but I can't remember where so don't quote me on it.
Originally posted by matiki You are correct sir.
Although this may seem true - slow charging may not be the actual reason.
Rechargeable batteries have premature failures due to over-heating - which occures mostly during charging - and fast charging is very suseptible to over-heating.
However in the case of NiMH (the most common rechargeable used these days) - a slow recharge rate is not really optimum - as the end of charge is not easily detected - then comes the problem of over-charging - which again is not good for the battery. Of course one can argue that with a slow charge rate it takes longer to over-charge.......
I do bow to the battery experts here but it may be worthwhile looking at
BatteryUniversity.com - specifically at their section on
Charging NiMH
about 2/3 down the page -
QUOTE:
"Charging nickel-metal-hydride Nickel-metal-hydride chargers require more complex electronics than nickel-cadmium systems. To begin with, nickel-metal-hydride produces a very small voltage drop at full charge and the NDV is almost non-existent at charge rates below 0.5C and elevated temperatures. Aging and degenerating cell match diminish the already minute voltage delta further. This makes full charge detection difficult. A nickel-metal-hydride charger must respond to a voltage drop of 8-16mV per cell. Making the charger too sensitive may terminate the fast charge halfway through the charge due to voltage fluctuations and electrical noise. Most of today's nickel-metal-hydride chargers use a combination of NDV, rate-of-temperature-increase (dT/dt), temperature sensing and timeout timers. The charger utilizes whatever comes first to terminate the fast-charge. Nickel-metal-hydride should be rapid charged rather than slow charged. Because of poor overcharge absorption, the trickle charge must be lower than that of nickel-cadmium and is usually around 0.05C. This explains why the original nickel-cadmium charger cannot be used nickel-metal-hydride. It is difficult, if not impossible, to slow-charge a nickel-metal-hydride. At a C?rate of 0.1-0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full charge state accurately and the charger must rely on a timer. Harmful overcharge can occur if a partially or fully charged battery is charged with a fixed timer. The same occurs if the battery has aged and can only hold 50 instead of 100% charge. Overcharge could occur even though the battery feels cool to the touch. Lower-priced chargers may not apply a fully saturated charge. Some will indicate full-charge immediately after a voltage or temperature peak is reached. These chargers are commonly sold on the merit of short charge time and moderate price. Simple Guidelines: Avoid high temperature during charging. Discontinue the use of chargers that cook batteries. A charger for nickel-metal-hydride can also accommodate nickel-cadmium, but not the other way around. A charger designed for nickel-cadmium would overcharge the nickel-metal-hydride battery. nickel-based batteries prefer fast-charge. Lingering slow charges cause crystalline formation (memory). nickel- and lithium-based batteries require different charge algorithms. The two chemistries can normally not be interchanged in the same charger. If not used immediately, remove the battery from the charger and apply a topping-charge before use. Do not leave nickel-based battery in the charger for more than a few days, even if on trickle charge. A well-designed charger is a reasonably complex device. Taking short cuts will cost the user in the long run. Choosing a well-engineered charger will return the investment in longer lasting and better performing batteries." END QUOTE
Back to the original question - primary lithium batteries (like the Energizer e2) do last longer - but they are not rechargeable and are expensive.
Most people recommend using NiMH rechargeables - normally the higher the capacity the better - however some people have found higher rates of failures of higher capacity NiMH (like 2500mAh) to the point where some people have preference for slightly lower capacitie like >2000 mAh - BUT these are not definitive - but fast chargers that fail to detect end of charge thus over-heating and over-charge may be the culprit.
ref:
More dying Energizer 2500's... Duracell 2650 batteries dying
C/2 rate of charge for NiMH seems to be some kind of "optimum" (read section above) - it seems the lowest rate of charge where end of charge can be reliably detected, and with a functioning charger the charge is stopped or changed to true trickle charge for NiMH (ie: =< 0.05C).
However the main complaint of NiMH is their high self-discharge rate - often people return to thie cameras some months later to find the batteries flat.
The new LSD - Low Self-Discharge batteries appear to be gaining favor - eg: Sanyo eneloop, Ray-O-Vac Hybrid, Kodak Pre-Charged, Uniross Hybrio.
Apparently the Sanyo eneloops are different from the others. Eneloops have very slightly lower capacity (although the rating seems very accurate) - but seem to hold their charge longer. Eneloops are the most popular because of name recognition - but reports on others are all favorable - but beware these are all relatively new on the market.
My personal "strategy" is to use high capacity NiMH ~2500mAh when I know I have to shoot a lot over a short period of time and keep a set of LSD batteries (I use the Kodak Pre-Charged mainly because they are cheap) as back-up/spare.
If I am not going to use the camera for a while - I then keep the LSD/Kodak Pre-charged in the K100D.
Some references on LSD -
Eneloop Self Discharge study - CandlePowerForums new Kodac "Pre Charged" NiMH batteries?
see posts
#13 ,
#14 for comparison graphs of capacity between the Kodaks and the standard Duracell 2650mAh NiMH, and against the Uniross Hybrio (LSD).
--
Vincent
http://UnknownVincent.Shutterfly.com Unknown Vincent Photos 2006 Unknown Vincent's Photos 2005 Unknown Vincent Photos 2004 Unknown Vincent Photos