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68k PowerBook battery calibration issues

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I have rebuilt batteries for my PowerBook 170 and my Duo 280c (with a type I battery). I used cells with higher capacity than the originals.


The problem is that even though the battery meter shows over 80% carge (after running for approx. 10 mins), the low-power warnings comes up and the computer goes to sleep. Seems like MacOS does not understand that the battery still has a lot of charge.


Any ideas ?

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AFAIK the batteries used in Pre-G3 powerbooks were pretty "dumb." That is, the only way they detected charge is via measuring the output voltage - the battery itself contains no special hardware. On 1400 series batts, the ID board is only a transistor and some wiring - The duo batt is probably similar. The 170 batt has no ID hardware at all as I gather.


The charge meters on PB's tend to be VERY inaccurate, unless the battery is discharging from a full charge. You may actually have only 10% charge when the PB says 80% - check the actual voltage with a voltmeter. I've found that most NiMH PB batteries have an output voltage that is 1.0 to 1.5v MORE than the rated voltage. For example, my 1400 batts, while rated for 9.6v, put out about 10.35v when fully charged. Once the batt dips below that rated voltage, you very rapidly approach forced-sleep and warning messages territory - 9.0v seems to be the lowest a 1400 batt can go before the laptop just clunks out.


That said, I recommend you give your rebuilt a good, two or three hours charge, and then measure the output voltage. Like I said, it should be 1 or 2 volts HIGHER than the rated voltage. If it's AT the rated voltage, or very close (within .1v), then it doesn't matter HOW much mAH your batt offers - the voltage will dip below the rated voltage earlier than the PowerBook might expect, causing it to think that it's batt is dying.

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