Battery problems

rca@rle-vlsi.mit.edu
Fri, 5 Jun 92 13:00:39 -0400

> Hi. I have just received my UltraLite from IME. I hooked everything up and
> started charging the batteries. After about 7 hours the charge light was off,
> so I unplugged and put it in my briefcase to use today (I'm sure the unit was
> off).
>
> When I turned on the unit this morning, I got the power fail message during
> startup. So I plugged in the charger and the charging light stayed on for
> about 5 minutes before going off. Unplugged the charger; got the power fail
> message immediately. While the thing is sitting there the charge light comes
> on every couple of minutes.
>
> I measured 13 volts across the open-circuited removable battery.
>
> Is something wrong with my battery? Did I just fail to charge it long enough
> the first time, even though the charging light went out (the manual said the
> first charge might take 16 hours!)?
>
> Thanks,
> Kip Ingram

The 7-hour charge is about right for a battery which was discharged in
normal use. The 16-hour number is for a battery shipped completely
discharged.

However, your battery seems to be doing something similar to what one of
my batteries did when it died. It would appear to become fully charged,
but wouldn't run the machine very long. Try charging the battery until the
light goes out, then take it out and measure its voltage with a low-valued
resistor across the terminals (a 50-ohm, 5-watt resistor, if you can get
one -- 470 ohms, if you can only get 1/2 watt ones.) The voltage should
start out at 13V or above and drop down to about 12V but should decrease much
more slowly after this initial drop. The Ultralight fails to boot at about
10V or so, I seem to remember.

There's a possibility that the charger is not working right, but I think
a dead battery is more likely. You can double check by getting a second
battery (handy to have anyway) and trying it out. Hopefully IME will
replace the first battery, if it proves defective.

Good luck,

Bob Armstrong
Research Laboratory of Electronics
MIT, Cambridge, MA 02139
Email: rca@rle-vlsi.mit.edu