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Hello,

I got a Motorola NiMH battery for a Talkabout radio. It is 3.6 V, 1400 mAh and very close in size to the Classics power pack.

I checked its size on my HP-65. Acouple pads in the sides (like tha batteries Mike Hoskins sells) and it fits in the battery compartment. But...

There is no indication on Classic calculators battery pack polarity, and I am afraid of any damage due to wrong installation.

Now the questions.

Is it safe to use this battery on a Classic calculator? Which terminal is positive and which is negative on the calculator?

Thanks in advance.

You can use the battery but I would not recommend charging it with the original HP charger - they are not suitable for NiMH cells as it is not voltage limited.

Terminal polarity of all classics is the same, here is a poor example but it is all I could find, the (-) is towards the top of the unit, the (+) terminal is toward the label.

Top terminal is negative (-) and bottom is positive (+). It is safe to use any battery, provided the voltage is correct, which in your case it is. However, the HP charger was not designed for NiMH batteries, so I can't say if charging might not damage it.

Hello,

Thank you so much.

Fortunately I have the HP Reserve Power Pack Charger, and I do not charge batteries within the calulator. Using it helps a lot, no worries about fried ICs.

I did try to use the charger with the Motorola battery but since it is smaller than HP packs (without pads) it simply does not fit.

Chargers for NiMH batteries are easy to get. That is the next step. Then I will put a couple pads on the battery to test it. I will post my progress on this.

Quote:
Fortunately I have the HP Reserve Power Pack Charger, and I do not charge batteries within the calulator. Using it helps a lot, no worries about fried ICs.

The "Reserve Power Charger" is a totally passive device, all the electronics are within the wall plug in so there is no difference if the batteries are in the calculator or reserve pack, it is not advisable to charge NiMH cells with either method. A proper, external NiMH specific charger is the only solution.

It is 100% safe to operate classics without card readers from the charger with no battery in place. Stated in the reverse, the 65 and 67 must have a battery in place to operate safely with the charger connected.

Hope that helps.

Hello,

Thank you for the safety tip.

Since reading a similar warning on the HP-65/67 Owner's Manuals, I never charge batteries with the calculator.

I just got a Motorola charger for the NiMH batteries. I will add some padding and test them when I get back home in a few days.