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HP41 rechargeable battery packs issue - Printable Version

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HP41 rechargeable battery packs issue - aurelio - 09-13-2016 10:08 AM

I rebuilt a few years ago a couple of battery packs, following the tips found here and somewhere on the web. Then I forgot them in a box, for a while, using mostly alcaline N cells.

I've tried to recharge recently them with a 82066B charger, but there's no way to do it
On the first one I can measure just 4,25 V, on the second 5,67 V
with the first, the calculator even does not turn on, while the second does not allow the card reader usage.

I've swapped the charger with another spare (both they supply 12,5 V AC) but there's still no way; now I have to arrange to check the current supplied by the transformers.

I did not read before this post

"WARNING: the old chargers charge the nicads at about 14mA, the newer ones at 16mA (which is also their peak current at 6V) which is WAY TOO MUCH for those tiny nicads. So if you've got nicads in the pack, DONT LEAVE THEM ON CHARGE TOO LONG. 16mA is about a 4 hour charge rate."

I left last time a whole night both the packs in charge Smile

I have so to re-open the packs and check again, what do you expect I can find out?

I suppose to have not harmed the batteries with charging, what is their average life time?


RE: HP41 rechargeable battery packs issue - Sadsilence - 09-14-2016 07:02 AM

Depends on what is "for a while in a box". Normally NiCD or NiMH batteries can be used for 10 years or longer, when they are really used and charged regularily. Unfortunately due to self discharge "feature" they get totally empty within about a year. And a deeply discharged battery is a gone battery. So I guess you have to rebuild your battery packs again. There are 1/3 aaa nimh cells around with a capacity C of about 150 mAh. Fits perfectly to charging current of 15mA. With C/10 for about 15h NiMH/NiCD cells are charged the best way and even 24h or 48h do not harm.