Rechargeable Batteries questions

[longers]

I've got a few questions about rechargeable batteries.

Having read a few recommendations from people about the Eneloop batteries and chargers I would like to get a set of 4 AA and 4 AAA complete with charger.

The batteries I have seen for the Eneloop are 2000 mAh. I don't know what this means (the mAh bit). I've seen other re-chargeable batteries listed at different mAh.

Does it refer to the size of charge of the battery ie run time or is it something else? What is mAh and is it important?

Could I run different makes of re-chargeable battery in an Eneloop charger at the same mAh?

Could I run different mAh batteries in an Eneloop charger?

Could I get the Eneloop batteries and use a different charger?

I'm a total electrical dunce so need things explaining in very simple language please.

Thanks in advance .

 

[Chuffy]

I'm a complete dunce too, so take this like a Scotsman takes his porridge...

The mAh refers to the storage capacity of the battery. 2000 is a little on the low side. I think they go up to about 3000, mine (from Maplins) are 2500. I'm not sure how that equates to runtime though and whether it just scales up (eg, 1000mAh = 1 hour, 2000mAh = 2 hours etc). Be warned, larger capacity batteries can be slightly fatter than normal, worth checking if you have a tight battery compartment (and the Tesco 3w torch is a bugger for this - see various threads).

Chargers will work with any rechargeable battery. All they do is feed current through. A smart charger (and don't get any other kind) will fill up to 4 AA battery in about an hour and will switch off when the batteries are full. It won't matter if those batteries have different mAh ratings. The charger will also have a discharge button, which will drain the battery before recharging. This is important due to the memory effect. Not quite sure how to explain this properly, but basically if you charge your batteries from partially full you can knacker them. This is all you need to know...

I'm sure someone will come along and tell me that I've just posted a complete load of cobblers, but my batteries and charger have been well used and happy for the last year, so it can't be rocket science...

 

[longers]

Thanks, I understood that

Maybe I'll look at a different make of batteries and charger then as all I can find for those is 2000mAh. Unless someone else knows different?


I have read about the different sizing issues with regards to the torches.

 

[Crackle]

Charger discussion here http://www.cyclechat.co.uk/forums/showthread.php?t=21832. Far more info than you can possibly digest and I use GP batteries

Oh and Lithium and Nimh batteries don't really suffer from memory effect, though NiCADs do. Chuffers is old though and is probably thinking of NiCADs

 

[Panter]

One big plus with the eneloops is of course that they hold charge.

When I bought my brace of Hope 1 LED lights, I cleverly rushed out (Ok, sat on arse and clicked the mouse) and bought the biggest batteries I could find at 2900 mah (milleamp hours. ie, the the maximium amperage they can supply for an hour before flattening.)

They're great, and last ages although the downside is, like all Ni-MH they loose about 10-15% charge a week so need a fresh rechardge before using whereas the eneloops would be charge and forget so are actually more practicle in the real World.
Unless you really need a huge power delivery of course, what are they for?

 

[Panter]

Oh, there's load of info here about chargers, it's brain frying stuff though

 

[MajorMantra]

One big plus with the eneloops is of course that they hold charge.

This is pretty important. A 2000mAh Eneloop is a lot more useful than a 2800mAh old-type nimh. Also, different cells have different internal resistances so a high quality (low resistance) nimh may well give better endurance than a low quality one that craps out under load.

By the way, I'm new here. Hi!

Matthew

 

[LondonCommuter]

Eneloops are great because they hold their charge (I think they claim to be 85% charged over a year) so you can trust them over the summer when you might only be using your lights now and then. I've had them for 1.5 years and never had any problems. THe USB charger is handy for work too.

 

[ColinJ]

The mA is an abbreviation for milli-Amp. 1 mA = 1/1000 Amp. Amp is short for Ampere, the international unit for electrical current.

The h is short for hour.

xxxx mAh is a measure of the capacity of the batteries. It simply means that a battery could provide a current of xxxx mA for 1 hour, xxxx/2 mA for 2 hours and so on.

NiMH is short for Nickel Metal Hydride which just describes what they are made of inside. It is the successor to the old NiCad type (Nickel Cadmium). It is better for the environment because Cadmium is nasty stuff.

I have some 2700 mAh NiMH batteries for my Garmin GPS. It has a nominal current drain of 100 mA (when not using the backlight) so in theory freshly charged batteries should last for about 27 hours of continuous use which is more than I'll ever do in one go. (I might one day do a '300' or maybe a '400' but '600' or more kms isn't something that I aspire to!) I left the GPS on for 24 hours once and it was still working so I think the figures are about right.

What else...? Oh yes, I think that it was mentioned above - NiMH cells tend to discharge themelves relatively quickly so they are useless for things like clocks which need a small current for a long time. NiMH is for higher currents and shorter times - GPS, cameras, lights and so on.

I'm sure that I read somewhere that NiMH suffer from the cold! I can't find the article now, but I remember thinking that it might be a factor on winter rides. The last thing you want is for your lights to pack up unexpectedly. Speaking of which... NiMH die very suddenly! You don't get much warning when they are becoming discharged because they hold their voltage up well into the discharge cycle. That's another reason for starting with freshly-charged cells. If I'm going to be using my GPS or camera, I charge the batteries overnight before use.

PS Hi Matthew!

PPS Just noticed - you weren't asking about NiMH were you longers, but it's all useful info isn't it ? Those Eneloops sound handy. I might get those instead of NiMH next time.

 

[MajorMantra]

I'm sure that I read somewhere that NiMH suffer from the cold! I can't find the article now, but I remember thinking that it might be a factor on winter rides. The last thing you want is for your lights to pack up unexpectedly. Speaking of which... NiMH die very suddenly! You don't get much warning when they are becoming discharged because they hold their voltage up well into the discharge cycle. That's another reason for starting with freshly-charged cells. If I'm going to be using my GPS or camera, I charge the batteries overnight before use.

PS Hi Matthew!

The thing about the cold is absolutely true and of all battery technologies I think nimhs are the most susceptible, though the newer ones may be better, I'm not sure.

If you were dealing with serious cold then blocking off your batteries' cooling (if there is any) would help though for the typical bike light application this is probably overkill.

Incidentally my knowledge of batteries comes from years of being a model aircraft geek, a hobby where people are particularly cruel to their batteries and where peak performance really matters.

Thanks for the greeting Colin.

Cheers,
Matthew

 

[simoncc]

Oh, there's load of info here about chargers, it's brain frying stuff though

Why not just forget all the technical stuff and carry a spare set of rechargeables in your pannier? That's what I do. So long as you cycle in the dark regularly, which a winter commuter is likely to do, then you won't be caught out by discharged rechargeables. NiCd and NiMh ones are still good for the job, but if you are buying for the first time then there's no reason not to buy eneloop or the other brand equivalents if you can afford them.

As for all the complicated charging advice, forget that too. If you have an old charger just charge them fully every time. You'll still save loads of cash.

 

[jimboalee]

NiMh suffer 0.002 V/Deg C when getting cold.

When you take them out of the charger at 50 Deg C, they might read 1.39 V on a DVM. Put them in a Garmin eTrex and after riding for 1 hour with zero deg C wind again and they will stabilise at 1.29 V.
When the voltage would have been 1.25 V at 16 C, at 0 C, they are 1.22 V. Four hours later ( 5 hours total ) they have reached 'mid-point' nominal 1.2 V but at 0 C, they are 1.6 V and the Garmin is bleeping and flashes up "Battery Low".
You will check and there is only 1 bar of the battery indicator left, after FIVE hours!

 

[longers]

Thanks all, I'm a bit clearer about a few things now.

Welcome to MajorMantra too .

 

[Panter]

Why not just forget all the technical stuff and carry a spare set of rechargeables in your pannier? That's what I do. So long as you cycle in the dark regularly, which a winter commuter is likely to do, then you won't be caught out by discharged rechargeables.

I agree completely. Does depend on the intended useage though. For me, I use mine for infrequent off-road MTBing so the charging thing is more of an issue.

We've just moved premises at work so I'm hoping to be able to commute a lot more regulary so I'll hopefully be able to reap the benefits of my 2900mah batteries

 

[marinyork]

Started using NiMhs in the rear lights permanently now. The hybrios I have perform better than the alkaline batteries in the rear. The old uniross rechargables I had were useless in the rear cateye so it was a surprise that the next generation function so well. I got about 20hrs of really bright light out of the hybrios before fading. Going to do another measurement to see if it was longer than this. Upon putting in the spares last time discovered the alkalines were no where near as bright as the hybrios before they faded.