Cells in Batteries

[JavaScriptDonkey]

My experience is that recyclable batteries are not very good when used in torches. They drain faster and plummet quickly at the end.

You also need 2 sets per application so you can use the device while they recharge.

Great for low draw stuff like remote controls though.

What you need is a re-chargeable lantern with its own PV panel built in.

[adam2]

The cheaper rechargeable batteries have a very small capacity when compared to disposable alkalines.
The better ones have a greater capacity, but do of course cost more.

Re-chargeable 6 volt lantern batteries do exist, but again tend to have a reduced capacity.
Some types are 6 volt lead acid, these give a full 6 volts ON LOAD unlike the 4.8/5.2 volts average on load voltage of disposables. This may require that the 4.8/5.2 volt lamp be replaced with a 6 volt one.

nicad lantern battery---------------1.2 A/H
Lead acid lantern battery-------------4.0
cheap zinc carbon lantern battery---4 A/H
Good zinc carbon lantern battery---11 A/H
UK spec alkaline lantern battery-----13 A/H
USA spec alkaline lantern battery----27 A/H

Cheap D zinc carbon------------------4 A/H
Good zinc carbon D cells-------------8 A/H
Duracell D-----------------------------18 A/H

I know which I would prefer in any long term emergency or disaster !

[adam2]

What you need is a re-chargeable lantern with its own PV panel built in.

A powerfull enough PV module to charge a reasonable size battery in one day is too big to build into the lantern.

Sollatek make some very good ones with a seperate PV module that plugs into the lantern for charging.
Expect to pay AT LEAST £100 for a qaulity PV charged lantern, perhaps twice that much for a bright long run time one.

Minimum size flourescent lamp for good working light is about 7 watts
Allowing for ballast losses, say about 0.7 amp at 12 volts.
6 hours use will consume about 4.2 A/H
To charge the battery will take about 4.7 A/H
To reliably produce 4.7 A/H in one day will need about a 20 watt module in tropical conditions or as much as a 100 watt module in UK winter conditions.
A 100 watt module is just about portable, and a 20 watt one is easily portable. But too big to build into a lantern.

[mobbsey]

cheap zinc carbon lantern battery---4 A/H
Good zinc carbon lantern battery---11 A/H
UK spec alkaline lantern battery-----13 A/H
USA spec alkaline lantern battery----27 A/H

I think that you might like to put a "milli" prefix in there somewhere!!

I think you're also missing the more basic issue here, which is that the idea of routinely using disposable cell batteries is flawed, irrespective of how much more convenient they are compared to the alternatives. We don't have the energy and resources to manufacture disposable toxic wastes any more, whether people accept that fact or not. If you've been watching the prices of alkaline cells climb recently, that's slowly hitting home but it'll become far more pressing in the next few years.

[adam2]

No need for a "milli" prefix, I believe that the battery capacities are as stated in ampere hours.
A Duracell D cell is about 18 ampere hours, that is it could supply one tenth of an amp for about a hundred and eighty hours.

This could be expressed as "eighteen thousand milli-ampere hours" and sometimes is because it sounds more.

[mobbsey]

A Duracell D cell is about 18 ampere hours.

Lead acid batteries are stated in Amp-hours (Ah). Most rechargeables are express in milli-Amp-hours (e.g. 2,400mAh == 2.4Ah), possibly to make it look like a bigger number! But for the average person they wouldn't know the difference between Ah and mAh, so it's a good idea to keep the same units that are used "on the tin" to avoid confusion.

However, the discharge characteristic is equally important to the overall effectiveness of the cell as its capacity. Thus the true capacity of a D-cell is somewhat different. At the optimum discharge rate in a laboratory you might get 15 to 18Ah, but in real life, turning a torch on and off, you're lucky if you get two-thirds of the figure stated "on the tin". The laboratory test also takes the cell down to about 0.7 or 0.8V, whereas a lot of electronics (e.g. MP3 players/digital cameras) will often cut out above that figure -- meaning even more of the capacity is wasted. I remember in the 1980s seeing interesting switched mode designs so that you could run a battery down to about 0.5V (as I remember the limitation is the bias voltage of the transistor used) so that you could get more power out of the cell.

As noted by someone earlier, rechargeables tend to cut out very quickly. That's because they have more of an S-shaped discharge profile, so by the time they cut-out you've pretty much emptied the cell. In contrast the elongated slope of the alkaline discharge profile can mean that you may still have a lot of unused capacity when your equipment browns out. See this article for some comparative graphs -- http://www.powerstream.com/AA-tests.htm. In fact this also demonstrates the great difference in effective capacities when the cell is discharged at a different rate, but that NiMH cells tend to produce the same output irrespective of the rate of discharge.

[clv101]

I reckon we should ban (or at least tax to the same price as decent rechargables) alkaline AAs.

See this thread about Eneloop rechargeable:
http://www.powerswitch.org.uk/forum/vie ... hp?t=19585

[emordnilap]

I bought some Eneloops on-line for our head torches and they are pretty good, the charge much longer lasting than the Energiser ones we were using. In fact, the Energisers were crap.

So, an improvement.

[biffvernon]

Reviving this old discussion - any suggestions as to what the best brand of rechargeable batteries is? Small ones - AA and such-like.

[emordnilap]

Reviving this old discussion - any suggestions as to what the best brand of rechargeable batteries is? Small ones - AA and such-like.

Eneloop get my vote (and clv101's); they beat all the other rechargeables I've tried into a cocked hat, even the Duracell ones. I suspect Duracell benefit more from their advertising than their quality.

[biffvernon]

Thanks.

[biffvernon]

eneloop or eneloop pro?

[emordnilap]

Ah. I've only bought the basic Eneloop but if you've any experience with smaller rechargeables, you'll probably find either to be quite a definite step up in quality and 'delivery power'. This is in spite of their rather daft name.

A quick glance at a reseller's website tells me that regular Eneloops recharge 2100 times, whereas the Pro only 500. Hmmm. The ones I use in my head torch (regular) have probably been recharged 200 times already, so the Pro would have almost reached half their life by now.

[biffvernon]

Yep. But they hold a bit more. Hmmmm.

Panasonic’s Eneloop Pro unique features at a glance
- Low self discharge rechargeable battery.
- Minimum capacity 2450 mAh, nominal capacity 2550 mAh (that's why it says 2450 mAh on battery, it's MINIMUM capacity)
- Provides high power performance down to sub-zero temperatures (as low as -20°C).
- Can be recharged up to 500 times.
- Combines the best features of AA alkaline (ready for use) and rechargeable (reusable) batteries.
- Factory pre-charged by solar energy and ready to use right out of the package.
- Maintain 85% of their charge after 1 year of storage, 70% after 5 years storage.
- Stable voltage with longer power life than alkaline batteries.
- No memory effect – batteries can be recharged when fully, or partially drained.
- Provide long lasting power while saving costs.
- 100% genuine, made in Japan, highest quality guaranteed.

[clv101]

I reckon we should ban (or at least tax to the same price as decent rechargables) alkaline AAs.

Hmm, my position from three years ago, remains unchanged. Anyone who's bought an alkaline AA in the last three years made a mistake.