hp 41c battery pack replacement


I have been using LiPo batteries for my RC hobby and it occurred

to me that 2 or 3 very small LiPo packs (3.8mm x 15mm x 33mm) in

series coupled with a small BEC (reduce 7.4V/11.1V down to 5.5V)

could feasibly fit in the battery compartment. These small LiPo's

are 130mAh and with the BEC would yield a major increase in over-
all pack capacity. Getting a charger for this would be very easy,

however refitting this into the existing battery holder may be the

big show stopper.

So, what do you think? Does this sound nuts? Sounds like a major

reengineering project to me, but winter is coming...

I appreciate all input.


Capacity is not the issue with HP41 batteries (unless you are using the card reader a lot). N cells usually last over a year. Self discharge of most rechargable batteries means you will be charging them monthly. If you have to take your modified pack out of the machine to do so, then you might loose memory,


The main issues for me is leakage, the CX or a C/CV with a timer module draws enough current to slowly flatten nicad bateries to the point where they leak chemicals without even indicating "lowbat".
Once this happens you may get some corrosion in the battery compartment.

You can get nicad N cells. Retrofitting something else at a different voltage is possible but I don't see much point in it except to save a few bucks...




Where can we get NiCa size N?



Try an alarms system company, or a battery specialist.

NiCad N size bateries are available.



Mouser www.mouser.com is one of the big distributors in the U.S. that sends thick paper catalogs (1500+ pages) to everyone in the elctronics industry and a lot of hobbyists every couple of months. They have Sanyo NiCad N cells as catalog number 639-N150N.

My 41cx (which BTW includes timer module, built in) goes a year or two on a set of alkaline batteries. Even when it was getting used all day every day controlling automated production testing almost 20 years ago (plus some other work in the late evenings), a set of alkalines lasted weeks. The low-battery indicator goes on when the batteries are down to about 1.2V, which is almost what you'll get from NiCads when they're fully charged. It wouldn't be worth fooling with them, especially since they have a pretty high self-discharge rate, unless you were constantly using the card reader or the optical wand (or both).


Couldn't agree with you more, Garth.

My Nicads didn't last as long and caused me some grief.

Another idea that is good in theory but fails in practice.



I have seen that NiMH cells have a very low self discharge rate. They last a lot. I have battery packs refurbished with 1/3AAA (150mAh) that work fantastic. As I couldn´t find NiMH N sized cells I bought also 2/3AAA NiMH cells (300mAh) which are same lenght as N but 10mm diameter instead of 12mm. I have compensated the diameter with a plastic tube and I am using them in my 41CX. That is the best solution that I have found. I have to charge them outside the calculator but I can do it in 1h with a fast charger. I have two sets of those cells so I don´t lose the memory.


Actually NiMH cells tend to have a slighly higher self discharge rate the NiCads...


Hi !

I have about 100 "N" size NiCd batteries (190 mAh) and I have no use for them, if you or anyone else reading this thread needs a few, just let me know and I will send you some...(shipping is on you).

Please note... I am NOT selling these cells, I have no economic interest in this, I am just trying to help.



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