Battery matters

[Davey]

Q. 1. There is an item in one of those advert. booklet things that come with the Radio Times or whatever. It offers to recharge normal batteries, up to 10 times, and up to 90% of their original capacity. Is this:=20 a. possible;=20 b. possible, but optimistic;=20 c. a load of b....cks;=20 d. any of the above, and Dangerous with it? If it is true, it would be worth buying, but at =C2=A325, it would need to be very good.

Q. 2. If the battery in my DECT 'phone can stay on charge for years, with only very rare and short periods of use, and still stay in good condition, why can't the battery in my laptop PC do the same?

--=20 Davey.

[charles]

I suspect that if your laptop had a battery that behaved in the same way as your DECT phone, the battery would be a lot bigger and heavier than the one you have at the moment.

[michael adams]

[Dave Plowman (News)]

Which? tested this idea some years ago, and concluded if you re-charge the battery long before it is flat, it will recover to some extent. But not in the normal way of recharging when the battery is near exhausted. Their conclusion was it wasn't worth the bother.

There's no reason why a charger of this type should cost much more than one for 'ordinary' rechargeables - say something under 10 quid - so it's doubly a con.

Why do you want to attempt to re-charge disposable batteries anyway? Proper rechargeables which can be cycled hundreds of times ain't expensive these days - perhaps twice that of premium alkalines.

[Brian Gaff]

Question 1, the dry battery charger idea has been around since at least the

60s when a circuit for a home made one was in Practical Wireless. The trick is not to flatten the battery, just use it a bit then trickle charge it with quite a rough DC but limit the current so you don't bust open the battery. The reason most batteries die is a pollution on the electrodes that cannot be reversed. Most of these reactions in batteries are reversible but if there is very little working contact to the electrolyte it won't ever happen, hence the only use a bit thing. I have found that Alkaline work best in this respect. However rechargeable alkaline are made now with more secure seals, One of the dangers in doing this charging is leakage. Brian

[Brian Gaff]

I've not found laptop batteries to be much of a problem as long as the charging circuit will stay working correctly, it protects it. I must beg to differ about the rechargable phones, most seem to have one cell that goes down and then you need to replace it.

Brian

[Dave Plowman (News)]

My laptop was left plugged in and hardly ever used on batteries. The battery died after a couple of years.

My mobile phone is older - and also left on charge for much of the day - its battery is still fine. Only difference is it does get at least partially discharged regularly.

[Graham.]

I'd quite like to see a scan of that advert if you could oblige.

I suppose it's a consequence of a triple-dip recession why this very old idea has resurfaced now.

In WWII people were advised to cook their U2 torch batteries in the oven to rejuvenate them, not that I am old enough to remember.

As I said recharging non rechargeable cells is an old idea. Google "Dirty DC charger".

[charles]

I was doing it in the early '50s and must have read about it somewhere.

[meow2222]

Phone: NiMH Laptop: Lithium People pay more for tools with Li batteries, but they don't last as well

NT

[Davey]

Does that mean, as it implies, that a laptop battery with NiMh construction would last much longer?

[Davey]

I can do a scan, check back tomorrow.

I have heard about the batteries in the oven trick, and I think I even used it once.

--=20 Davey.

[Davey]

The major use by far in this household for batteries is portable radios. There are two used mostly, both versions of Grundig Yacht-Boys. One, which uses 6-AA cells, decides that the batteries are too low for use, and shuts down, long before the other one, which only uses 3-AAs, has the same problem. I have finally persuaded the wife to take the ones from the 'early' radio and use them in the 'later' one. But even then, there is still plenty of life left in them after the radios are done with them. We have tried rechargeables, but they seem to last for an even shorter time before the 'early' radio decides that they are powerless; and then, always, they will start to last for shorter and shorter periods, and then one will die, etc etc. I doubt that I would actually bother to buy a charge for normal batteries, but it is interesting getting information from everybody, and reading the discussions.

--=20 Davey.

[Davey]

And a re-reading of the advert. does indeed show that it says it is for Alkaline batteries, well, it calls itself an Alkaline battery recharger, having enticed one in with the headline: "Recharge ordinary household batteries again and again". Then in the body of the verbiage, it refers to 'ordinary AA and AAA batteries'. No mention of leakage as a potential (!) problem.

[Dave Liquorice]

1.5v/cell for ordinary batteries. 1.2v/cell for rechargeables.

Running them too flat. Ideally you shouldn't go below 1v/cell on any cell. With series connected batteries one will always run out of puff before the others, this one then gets reverse charged and after a while objects.

[SteveW]

Are you sure it's dc? I'm sure the last time I saw such a circuit it was ac with a dc offset, hence giving a series of positive pulses interleaved with smaller negative ones.

SteveW

[Graham.]

You would think that in these litigious times, and with the prevailing health & safety culture, coupled with the fact that all zinc-carbon and alkaline batteries carry a notice on the lines of, "Don't recharge or babies will die", it would be awash with disclaimers.

Quite refreshing!

[Graham.]

I have already mentioned "Dirty DC" elswere in the thread.

I see they are an AC/DC tribute band too.

[Davey]

Go to:

the original advert. that is in the flyer de-emphasises the 'Alkaline' part, per my earlier description. The actual wording is different, but the gist is the same.

--=20 Davey.

[Windmill]

Has anyone ever tried putting a Schottky diode (reverse-biased) across each cell in an attempt to prevent reverse charging? They conduct quite well at about 0.4 or 0.5 volts, which might help.