Converting a 41C to run on CR2032‽‽‽

[burkhard]

Somebody on a certain auction site is selling a 41CV that has been hacked up to run on two CR2032. I'm not against modifications that improve things (especially if reversible), but this makes for a big loss in energy storage. Each CR2032 stores ≈220 mAh (3 V nominal). Each of the four alkaline N-cells is hold about about 1000 mAh (1.5V nominal). Rechargeable NiMH N cells hold about ½ the charge of the alkaline,≈500 mAh, (1.2V nominal).

If somebody were to come up with a trick HP41C replacement battery, it would probably best be a modern, squarish, rechargeable LiIon or LiPo that fills up as much of the battery bay as possible and could ideally be recharged in place. A unit that could be removed as an assembly to permit using the spec'd N cells if need arises would be preferred. Soldering jumpers to the flex circuit is not so great.

This "couple of little coin cells" scheme seem like a really bad idea. And don't even think about running a card reader... or flashing a 41CL.
I hope this mod doesn't become a trend.

Maybe somebody owns stock in a CR2032 battery manufacturer?

(see attached photo)

[edryer]

I agree.

I did once buy a TI-58C that the owner modified to use a cell-phone battery... it was quite an excellent idea as the life time was five hours or more, the battery was light, and it made for a better than the original solution, charging was also simple.

If I were to modify a 41C it would probably be the same way... cell phone battery.

[jonese]

My problem with cell phone batteries is that they are short lived, they're here a year or two, then gone the next with different form factors.

That's my main gripe with the Prime. One day, that HP format (aka the Samsung Galaxy S3 battery) will no longer be made. Then what? Seriously. What do you do when the battery format (and perhaps chemistry) are no longer being made? Custom design your own battery?

No doubt, the HP Prime hardware can surpass the lifespan of the S3 battery format.

AA's have been around for MORE than 100 years and no reason to think it's going away anytime soon. A slight change in battery voltage between Alkaline, NiCd, NiMH chemistries for sure, but basically the same drop in format.

Sure, energy density probably plays a major factor in battery selection. But I'd rather have a working calculator in 10 years with an available power source at the cost of a slightly larger device to hold the 4x AA's.

I'm off topic, sorry.

[StephenG1CMZ]

When the batteries are retired, it is POSSIBLE to power the Prime using readily-available AAA's...
http://www.hpmuseum.org/forum/thread-577...ht=battery
Excellent video!

[jonese]

Yea, saw that a few months ago.

Problems
1) What happens when you also plug the USB in? Probably need to bypass the USB charge circuit...
2) Wasted energy in stepping up/down to get the voltage the HP Prime expects.

At that point, it's probably easier just to power the Prime with an external USB power bank (does that work without the batter installed? Havn't tried).

[Joe Horn]

(10-29-2018 01:51 AM)jonese Wrote:  ... At that point, it's probably easier just to power the Prime with an external USB power bank (does that work without the batter installed? Havn't tried).

Yes, Prime runs fine with the battery removed when powered by USB cable (just verified that on HW rev C and D).

[Jlouis]

Back to the OP, what about using a card reader with those cr2032?

[Massimo Gnerucci]

(10-29-2018 04:31 AM)Jlouis Wrote:  Back to the OP, what about using a card reader with those cr2032?

Mmmm... forget it.

[aurelio]

(10-29-2018 07:11 AM)Massimo Gnerucci Wrote:  

(10-29-2018 04:31 AM)Jlouis Wrote:  Back to the OP, what about using a card reader with those cr2032?

Mmmm... forget it.

Sure, it was already a problem to use the card reader with the original battery pack.......