Battery Chargers

[AndyT]

A bit more expensive but I've just ordered the MAHA C808M charger - does 8 AA/AAA/C/D cells .

 

[mike_s]

Ouch... $70 bucks for that thing! and it doesn't include any batteries.

 

[Lightning Fish]

Dying batteries can also often be identified by just leaving them sitting around for a week or two after charging, and then measuring the voltages. If it loses significant voltage over a couple weeks, then it has an internal fault and is bad.

I bought Energizer's battery charger and NiMH batteries. I use them for my light and not a camera. The instructions state that the batteries will lose 40% of their charge per month.

Does anyone know how these things work? Do they discharge the batteries first then charge them? Or do they just top up the battery? To charge a battery to full takes 5 (or 4?) hours. So if the batteries are only half charged, will it take 2.5 hours to charge to full?

Bill.

 

[onfloat]

A simple load tester. Go to Radio Shack get a 100 ohm power resistor, a single cell batter holder and a simple volt meter. Attach the resistor to the "+" and the "-" sides of the battery holder. Insert a fully charged battery and use the volt meter at the same points that you attached the resistor. If the battery looses more than %10 of the voltage in a 10 second span it's on it's way out.

 

[Charlie99]

Does anyone know how these things work? Do they discharge the batteries first then charge them? Or do they just top up the battery? To charge a battery to full takes 5 (or 4?) hours. So if the batteries are only half charged, will it take 2.5 hours to charge to full?

Most chargers don't discharge them first. While some people believe that discharge-before-charge helps maintain capacity, all of the battery manufacturers that I've corresponded with, and all of the extensive tests my company has performed on batteries indicates that you are better off just topping them up after each use, with an occasional trickle charge to equalize the batteries.

Most fast chargers just shove a constant current into the battery while monitoring the charge voltage. When you hit full charge, both due to a temperature change as the energy goes into heat rather than chemical change, and because of change in chemistry, the change in voltage vs. time changes. In NiCd batteries there will actually be a decline in charge voltage as you hit full charge. NiMH batteries don't have as drastic a change, and most chargers just look for a zero delta V vs. time (i.e. a flat spot on the voltage vs. time curve) to terminate the charge.

I bought Energizer's battery charger and NiMH batteries. I use them for my light and not a camera. The instructions state that the batteries will lose 40% of their charge per month.

The loss of charge varies dramatically with temp. IIRC, the loss doubles with an increase of 10 degrees C. A battery at 60% of capacity has pretty close to the same voltage as a fully charged battery, so you won't know how much it has discharged until you use it.

OTOH, a common failure mode for NiCd and NiMH cells is "dendrites" -- little tiny filaments of metal that get formed between the electrodes of the battery, often when they are fully discharged or reverse charged. These dendrites will cause a battery to go flat over a 24 period or less.

Charlie Allen

 

[sylpha]

I read the manual for my camera & came across a statement that i should always make sure i have a good power supply before i charge my batteries. Being a technical ignoramus i asked a frieldly electronics engineer who explained that good battery practise will extend the life of the battery. It's the number of times you charge a battery that diminishes their life most, so a power supply which is interrupted (and that may simply be because it isn't plugged in correctly) the battery will interpret each interruption as a new charge and diminish the life. a battery should also be completly drained on a regular basis to extend its life.

 

[spstar]

http://www.steves-digicams.com/2002_reviews/maha_c401fs.html
here is reveiw on the one that I use really works nice can charge one or four from different states of discharge has a slow and fast switch also and I have found a bad cell during charging with it
all in all a nice compact charger