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- laptop battery recharging
April 21, 2008, 10:29 am
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It uses two batteries (second one is for BIOS):
-pa8725u (14.4V 2.2AH NiMH) shows 0,45VDC
-XZ0072P09 (6V NiCad) shows 0VDC
They are dead, but I'd like to just try to recharge them. Of course
there is no
original AC power supply. So, can I use standard
AC/DC converter (1000mA max)? Or maybe the 9V NiMh recharger?
Should I just connect + to + , set voltage to 12VDC and let it charge
for a while?
Re: laptop battery recharging
NiCad batteries often recover so it's worth a try.
NOTE: Since you do not know if the batteries are recoverable
and you do not have the correct charger it is *essential* that you check the
batteries almost continuously
for excess heat!!!! If they start to get hot...turn the charger off at once.
Your six volt battery could probably be charged with the 9v charger...
The 12v charger may not be able to fully charge the 14.4 v battery but may
at least be able to bring the voltage up a bit
Re: laptop battery recharging
There's no such thing as a "standard AC/DC converter (1000mA
max)". There are many different converters of both
regulated and unregulated and these have a voltage rating as
well as a possible peak floating voltage depending on
Maybe what 9V NiMh recharger?
You aren't giving us the relevant information.
You have batteries in an unknown state, some may be shorted
or reversed after having sat in equipment powered by them.
You need a current limited supply trying to trickle them. I
suggest you use an unregulated 12V wall wart, with a 120 Ohm
resistor in series with the battery pack for the 14.4V pack,
and a 470 Ohm resistor in series for the bios NiCad.
Monitor the batteries to ensure they aren't overheating, a
lot at first then periodically over several hours.
Periodically disconnect the charging circuit and check the
battery voltage. 6V NiCad is 4 cells, 14.4 NiMH is 11
If they are charging and none are shorted you will be rising
above roughly (4 - 1) * 1.45 = 4.35V for the 6V battery pack
and (11-1) * 1.45 = 14.5V for the 14.4V battery pack, after
a few hours. If either pack cannot go much above these
values, at least the shorted cell in the pack needs
replaced, but more reasonably the entire pack would need
I might suggest another alternative, that since you need a
supply for the whole laptop anyway, you instead work on
making or sourcing one then use that to try charging the
batteries as the laptop designer intended. Again you would
want to monitor temperature of the packs, though it is not
unusual for quick charging (of primary 14.4V pack) to cause
the pack to get a bit warm, just not really hot.
However, I know nothing about that laptop but if it is
ancient as you described, it seems you need to do one of two
things to reasonably use it:
1) Forget about runnning it off the 14.4V pack since the
pack is so old that it won't have good capacity anymore.
Focus only on replacing the 6V pack with a new one. This
would be cost effective.
2) Replace the 14.4V pack as well as the 6V, either a newly
manufactured (not just a seller claiming a replacement is
"new" as some shady dealers will call any unused battery
pack new even if it has sat and shelf rotted for years, they
must have a guarantee about manufacture date and often packs
have that date encoded on them) or by opening the pack and
reconstructing it with individual new cells.
It seems a bit cost and time prohibitive to do this to a
very old laptop unless you happened to already have suitable
replacement cells lying around, especially if you don't even
know yet whether the rest of the laptop works so IMO, it's
better to focus first on getting main laptop ac-dc supply to
test whether the rest of it works before investing in
batteries and even then, a lot of money on batteries for a
laptop may not be a good investment as really old laptops
may have other problems like dying HDD, etc, which make it a
money pit when new low-end laptops aren't very expensive