O/T(ish) B&D 12v batteries and charging

Having noted that my trusty old B&D 12v drill/driver and 12v combi are starting to lose some battery longevity I had a quick Google to see how much a replacement might be.
About £30.
Since you can buy a new 18V combi (albeit not a particularly special one) for under £40 this does not seem to make economic sense.
I also can't seem to find a fast/trickle charger which would allow me to eke the best remaining performance out of the current batteries.
One major problem with lower end drills is the 3+ hours to charge plus the requirement to then take them out of the charger after the 3 hours to avoid damage. Combined with the requirement to discharge the battery as far as possible before recharging this does give all sorts of useability issues.
If I could find a reasonable trickle charger I might consider buying one more batttery to keep two drills going as the batteries are interchangeable. However I can't seem to find anything via Google so far.
It has been suggested that if I made up an adapter I could use my Site (Makita) charger which is rated on the front as 7.2 - 18V. Does anyone know how good these chargers are at sensing the fully charged voltage of battery packs? It looks feasible to cut the wire leading from the wallwart of one of my two 12V chargers (in the middle to allow reconnection if required) and then connect to another lead which fits into the Site charger but I wouldn't want to go through all the hassle of making up a connector to the Site charger just to fry a battery.
I am assuming that the B&D 12V charger is a simple arrangement of a 240V/12V wallwart and then a thin wire which takes the 12V to the adapter which fits the battery pack. If there is more intelligence in the adapter which the battery pack clips into then the solution may not work.
Any information appreciated.
Also, would a motor cycle 12V trickle charger work if connected to the battery pack?
Cheers
Dave R
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David WE Roberts wrote:

however the replacement batteries may well be beter than the originals.
Also at least 75% of the cost of a cordless is in the batteries. The motors are cheap mass produced chinese junk, as are the gears and bearings. there is not a lot left.
If the cordless is of good quality and in good condition, re battery it for a much BETTER tool.
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On Tue, 8 Jun 2010 13:42:27 +0100, David WE Roberts wrote:

Find a motor driven time switch. Open it up and connect the motor after the switch contacts. Plug the charger into it and set to run for 3hrs (or whatever) when it switches off the charger and it stops.
Simples.
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Cheers
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Dave Liquorice wrote:

better still but a decent 'delta peak' nickel cell charger from a model shop.
charge times around 20 minutes are the norm: faster than that overheats the cells a tad.
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On 08/06/2010 13:42, David WE Roberts wrote:

Have you tried eBay? quite often a reasonable source for that sort of thing?

They are proper delta peak sensing chargers, and so are as good as you will find. They also support thermal sensing if the pack has the contacts for it (four terminal packs rather than two).

Try it with an old battery first if you are unsure. However I have charged my non Makita 7.2V richmond drill battery on the Mak charger many times without any difficulty.

Many "slow" chargers you get with stuff like this are about as crude as it is possible to make. Often nothing more than a transformer, a single silicon diode, and a resistor to limit charging current. Stuffing unsmoother half wave rectified DC into the cells. (it works fine if you slow charge at 50 to 100mA, but becomes a liability when going faster than that).

I expect if you peak inside it, it is nothing more than a harness for connecting the PSU to the cells.
Stick a DVM on the contacts when plugged into the adaptor (without the battery). You will probably see DC at something a good deal higher than 12V. Stick an old speaker across it in series with a 100ohm resistor and you will probably hear a nice 50 or 100Hz buzz (depending on just how cheap the rectifier is!)

Not ideal. NiCd and NiMh chargers ought to be constant current[1], whereas lead acid chargers are usually constant voltage.
[1] the crap ones aren't however
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Cheers,

John.

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On Jun 8, 1:42 pm, "David WE Roberts"

no need for that. in fact its wha causes most damage

making one's trivial, albeit usually unnecessary

no no!

the charger needs some basic control first, a vanilla wallwart wont have that. No intelligence needed to trickle.

no!
NT
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