Finally I got my HP-67!

[Artur - Brasil]

I got the message!
Well, my aproach is completely different of what you say.
No more Ni-MH batteries neither NiCd. They are difficulto to control the charge process, as you have to monitor the temperature and voltage on cells.
HP charges are just one transformer inside - completely no control - circuits in calculators are so simple that some times you see just a resistor to limit current.
I had one cassette reader destroyed because one cell was defective and the whole set got so hot that case of drive was bended by heat.
Also, the leakage is a painfull and destroy everything in his way.

No, no! Li-Ion batteries have much, but 1000% better charging control, and in very thinny reay-to-use boards, that are sold for a banana cost. Your calculator got discharged, get one cell phone charger and plug it in. Couldn't be more easy!

Don't use any more NiCD or NiMH batteries. Adapt all your calculators to Li-Ion batteries. They are lighter, less expensive, easier to charge and last more.

My sincere advice!
Artur

(01-08-2020 06:09 PM)Dave Britten Wrote:  

(01-08-2020 05:42 PM)Artur - Brasil Wrote:  Eneloops?
Li-Ion charge module like TP4056, the ones with OUT and BAT terminals inline are very cheap, they are small, very cheap and can charge small or even large batteries easily. They feet on back off battery compartment door, as I did.
The rest of space are free for battery. As I used two Bl-5F (950mAh each) in paralell, i believe I got 1900mAh.
What is the battery you are talking about? Put a link and I'll get a better idea about what you think.

Artur

Eneloop is a popular brand of NiMH rechargeable batteries. I use the AAAs in my HP 65.