Which rechargeable battery you prefer for the HP-41?

[mfleming]

(08-24-2018 12:44 AM)Garth Wilson Wrote:  However, I did recently buy 20 Energizer alkaline N cells, expiration date 2022, for $17 ($.85/ea) including shipping, and I saw even lower prices if you want to buy 50 or 100.

After spending nearly $40 on four rechargeable batteries and an unsuitable charger (thanks Dieter) I abandoned the rechargeable approach due to the low cost of disposables. I did have one Energizer leak on me though, so I've used Duracells (advertised as "for medical devices") ever since. Search on "Duracell N E90 LR1 MN9100" on eBay. Plenty of sellers, one of whom sells 10 for $11.99 with free shipping. I'd have to go through a lot of disposables before breaking even on rechargeables, spares, sleeves and charger!

~Mark

[Dieter]

(08-24-2018 12:44 AM)Garth Wilson Wrote:  Are there any that give much over 1.2V per cell? Because that's where my 41's BAT indicator comes on, and that's a pretty standard voltage for rechargeable cells that are supposed to be 1.5V substitutes;

Both NiCd and NiMH cells have a nominal voltage of 1,2 V which is defined by the battery chemistry. Actually it is something between 1,4 V and 1 V (when completely discharged). The HP41 works fine with this voltage. The original 82120A battery pack had regular NiCd cells, and the system was designed to work with these.

If your HP41 really turns on the BAT indicator at 1,2 V this sounds a bit out of spec. It should be more like 1...1,1 V. Or, more precisely, a bit above 4 V for the whole pack. How did you determine that value?

Dieter

[ijabbott]

(08-24-2018 12:44 AM)Garth Wilson Wrote:  Are there any that give much over 1.2V per cell? Because that's where my 41's BAT indicator comes on, and that's a pretty standard voltage for rechargeable cells that are supposed to be 1.5V substitutes; IOW, I basically can't use them. However, I did recently buy 20 Energizer alkaline N cells, expiration date 2022, for $17 ($.85/ea) including shipping, and I saw even lower prices if you want to buy 50 or 100. I got these: https://www.ebay.com/itm/Lot-of-20-Energ...2749.l2649 . (My ebay ID is wilsonmines, and I have no connection to this seller.)

Ni-Zn cells have a nominal 1.6V output, but they need a special charger, and I've never seen them in 'N' size. The 'BPI' branded AAA cells I tried a few years ago turned out to be pretty unreliable, and I haven't dabbled with Ni-Zn cells since.

[grsbanks]

(08-24-2018 06:01 AM)Dieter Wrote:  If your HP41 really turns on the BAT indicator at 1,2 V this sounds a bit out of spec. It should be more like 1...1,1 V. Or, more precisely, a bit above 4 V for the whole pack. How did you determine that value?

If the voltage was measured with the batteries OUTSIDE the calculator then they could easily give such a reading but, once IN the calculator that's drawing even only a small amount of current, can easily drop below the BAT indicator threshold.

For readings to be really meaningful, the voltage should be measured with the batteries IN the calculator.

[CY-CL]

(08-22-2018 04:54 PM)Dieter Wrote:  Isn't it? Take a look at amazon.de – here it says "on stock".

In stock are the "Black Fox" only. I asked several shops about the green ones with large plus pol. No longer in stock... replaced by "Black Fox" is always the answer!

[Garth Wilson]

I measured outside the 41; but I doubt 2mA of idle current when the calc is on is going to pull it down significantly. Also, when the indicator comes on, it makes virtually no difference if the calc is idle (2mA) or running a program (20mA).