Charging rechargeable batteries

[B91]

My last lot of rechargeable batteries finally gave up the ghost so I bought a pack of four AAs from Maplin. I still have the old charger and am wondering how long to give them as the pack says to observe charging time.

The batteries say 1.2V replaces Alkaline 1.5V, 2000mAh, charge before use 7 hours - 480mA

The charger says Output AA-2 x (DC 2.8V at 150mA 0.42VA)

Help!

 

[big-all]

i would say23hrs as its just under 1/3 or 30% the charge rate
but others may dissagree

 

[ekmdgrf]

I've never really paid much attention, just stick them on until I remember to take them off. Some batteries don't really like being over charged but I've never had a problem with NiMH's. Nowadays I have one of those fancy chargers that does it all for you.

 

[ericmark]

I use my finger. Basic charging with constant current if the energy is completing a chemical reaction then very little heat. Once the chemical reaction stops i.e. fully charged then all that energy goes in to heat. So once battery becomes warm it is fully charged.

Time will clearly change according to if fully discharged or just part discharged.

Some chargers designed for the old NiCad batteries discharge the batteries first before starting to charge them. This is not required with NiMh batteries.

The Delta V charger monitors the voltage looking for a peak as the voltage starts to fall again it knows the battery is charged. However this peak is not as much with a NiMh as with the older NiCad battery so some older chargers may not detect when the battery is fully charged.

There are may types of NiMh batteries even in the same package some are designed for long shelve life other for high output. Clearly where the battery is advertised as ready charged it has a long shelve life and you can charge and store but as you get to 2500 mAh often the battery will lose 10% of charge in first 24 hours even if not used. This need a charger which drops to a trickle charge once fully charged to maintain the battery. In the main the Delta V charger does this.

Another problem is the old NiCad were often only 700 mAh where new NiMh can be 2500 mAh or more (For AA size) and some old chargers use a time out system and can switch off before the new battery is fully charged.

My camera battery can sit in the camera for 6 months and still be OK. But my flash gun batteries (2 x AA) will be nearly flat after being left for just 1 month. I am sure if I paid enough I could get AA batteries which held the charge for longer but the problem is there is nothing written on the batteries to give shelve live. Clearly Pentax and Nikon both realise we want to be able to leave the camera for 6 month and it still to work.

Nikon have used chips to stop you using anything but Nikon batteries and Iphones will not even give you access to the battery to stop you using batteries which do not come up to standard.

 

[JohnW2]

Iphones will not even give you access to the battery to stop you using batteries which do not come up to standard.

I suppose that might be one of the reasons

Kind Regards, John

 

[ekmdgrf]

Iphones will not even give you access to the battery to stop you using batteries which do not come up to standard.

I suppose that might be one of the reasons

I was just thinking the same thing.

 

[ban-all-sheds]

It might be.

And one day the horse might learn to sing.

 

[B91]

All very interesting but is there actually anyone here other than big-all who is interested in trying to answer my question?

 

[B91]

I use my finger. Basic charging with constant current if the energy is completing a chemical reaction then very little heat. Once the chemical reaction stops i.e. fully charged then all that energy goes in to heat. So once battery becomes warm it is fully charged.

My four new batteries were warm after just one hour on charge, so what do I make of that?

 

[JohnW2]

I use my finger. Basic charging with constant current if the energy is completing a chemical reaction then very little heat. Once the chemical reaction stops i.e. fully charged then all that energy goes in to heat. So once battery becomes warm it is fully charged.

My four new batteries were warm after just one hour on charge, so what do I make of that?

It could, of course, mean that they were fully charged (they may have come fairly well charged).

However, I think eric has somewhat oversimplified the situation as regards temperature. In practice, batteries usually do warm up a bit whilst they are charging (whilst the 'chemical reaction' is taking place), but then heat up more rapidly, and reach higher temperatures, if left in the charger after charging is actually complete. One therefore needs a bit of experience to interpret how warm the batteries feel (and the temperatures achieved are likely to vary between batteries, and between chargers).

Kind Regards, John

 

[B91]

OK, seems it's a bit suck it and see. The charger is a Fameart PC02, probably made about ten years ago. A4s are charged in pairs with an LED for each pair to tell you whether they are charging or not. I don't know whether it's smart enough to stop if the batteries are fully charged so I'll just let it run until the lights go out, which will be after 15 hours unless there is an auto-stop beforehand.

 

[Taylortwocities]

Most of my good quality rechargeable batteries have the charge time & current printed on them.
I note that cheap ones only say to "observe the charge time and current". I guess its written on the pack that I threw away 2 years ago.

 

[B91]

I posted that information in my first post

 

[Stivino]

Your charger should have a built in timer.
http://tinyurl.com/o2w5rfh

 

[B91]

It has a max charge time of 15 hours, but as its charge rate is very different from the charge rate stated on the new batteries it is meaningless. It doesn't have any other timing mechanism, maybe the later PC10 does.