On Feb 2, 10:55 pm, "Tina K." <[email protected]> wrote: > On 2011/02/02 15:53, J.M.P.Hissel so eloquently wrote: > > > On 02-02-2011 21:14, Yersinia,[email protected], wrote: > > >> > and you buy a new one that tests good (with a voltmeter) > > No, a voltmeter is useless! You'll need a battery-tester (10/15 $/€ ?)! > > I believe Jo is correct. A voltmeter tests the voltage at no load, once > a load is put on the battery the voltage will drop. A proper battery > tester should give more accurate results. > > Tina > > -- Yes batteries do have a finite (though fairly long - i.e several years) shelf life (especially if kept somewhere cool), during which they can lose some of their available energy, due to internal discharge currents, and, though they will often test OK with a multimeter, when you put a load on them the voltage can drop significantly, especially if the load is drawing significant current. (like a filament bulb or a big radio). A PRAM battery is only supplying a few micro-amps when the computer is powered off - that's why they last for years - especially if that computer spends a lot of time on or sleeping - but since many batteries of we LEM'ers are using machines older than five years then original ones will be getting wheezy and breathless (metaphorically) - I bought 10 PRAM batteries at a good discount a year ago and have used about 6 in machines already (buying them one at a time is waaay too expensive). Those ten-for-2 dollars coin cells on a card can be a false economy too - they often don't last anything like as long as branded ones - bear in mind they are often produced where the duff leaky capacitors that plagued the 1.2GHz eMacs were made - and finally, yes I've had problems with multimeters giving false readings when THEIR batteries start to drop below 1.2 volts - really you need another multimeter to check your multimeter batteries ;)} I once tested two worn out batteries that 'read' 2volts each - until I tried them on another testmeter with good batteries and THEN they showed their true worth at 0.9 volts! Dan in Wales, UK
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