HP-25 left on for a long, long, while


Hello all,

I've been quite busy. So busy that, after three months, I noticed that my HP-25 has been left on. The last time I used it was at least three months ago. Yes, yes, all I need to do is pry up the battery compartment but, Woodstocks have the most difficult battery compartments to open. So, from your experience and expertise, what could happen to the battery and the compartment?

Thank you


Very cheap alkaline batteries or coal/zinc-batteries tend to leak after being depleted. Alkaline will be safe for usually 1-2 years (even the cheap ones), but I had a lot of batteries which have not leaked after 20-30 years. But better be safe than sorry - always remove the batteries, when the calculator will not be used within the next months. And don't buy coal/zinc-batteries :)


I've had even the best alkaline batteries leak on occasion. But I've never seen an Energizer AA or AAA battery leak, I've used hundreds of them over many years of use and abuse. I use these in my calculator collection and feel safe even if I accidentally leave them on, depleting the cells and ignoring them for years afterwards (which has happened a fair amount). They have near zero self discharge.

They are a lot more expensive than alkaline cells but if you rarely turn on a calculator to play with it's a one-time expense.

I also feel OK about leaving 9V alkaline batteries on old calculators that use those. Although they use 6 cheap AAAA alkaline cells inside, I've never seen leakage get through the outer metal jacket.


I have seen 9V leaks, so these do happen. However the leak itself is not huge, mostly damaging the 9V Clip, which is easy to replace.


Have the batteries leaked, or why is it difficult to open the battery compartment?

Usually it is very simple to take the battery pack out of the calculator. Once it is out of the calculator, you can simply cut the middle plastic part out with a sharp knife. Then you can pry the cells out without any further damage. Simply clean everything if necessary and replace the cells with either alkalines (do not use the charger in that case!) or new NiCads.


Usually it is very simple to take the battery pack out of the calculator.

I have an HP21 that had been dropped into sea water (or something similar) and then left to rot on it's own for a long time. On the outside, it looks almost perfect. But the batteries (the original NiCd pack) had swollen so much due to leakage and corrosion that the battery compartment was absolutely impossible to open. But that's no problem because you can simply undo the two screws under the rubber feet on the display side of the calculator. The housing will then come apart and the battery pack will fall out. In my case this wasn't of any use because the pcb looked like the Antikythera Mechanism fresh from the seabed.


Woodstocks have the most difficult battery compartments to open.

I totally disagree.


Okay.... Please advise. I'm pressing down while sliding the door downward (in the arrow's direction). What am I missing?


I used an HP-21 and an HP-25 virtually daily for 25 years, and, yes, it is often hard to get the battery pack out.

You are right to try to slide the battery pack forward in the direction of the arrow. I often found that my finger didn't work. I would then use a wooden stick (to avoid gouging the plastic) against the lip near the tip of the arrow.

In extreme cases, I would put a screwdriver in the slot at the other end of the pack and rotate 90 degrees. However, the risk of gouging is increased by doing this.

In either case, when the pack slides forward, the bottom of the pack should pop out of the calculator case.

Hope this helps.



I too had an HP-25 back in the 1970s and getting the battery pack out was a bear.


Put the calculator with the keyboard down in your left hand. Place your right thumb in the square with the arrow in the battery pack and slide it in the direction of the arrow. The back of the battery pack will pop up, permitting easy removal. To install, just insert the two tabs at the arrow side of the battery pack into the slots in the battery compartment and press down on the battery pack at the rear until it snaps in place.


I keep trying this approach. The pack will slide and I will hear & feel the pop. But, it never jumps out of the spring. I want to press down harder to engage the spring but, again, I must be missing something. Besides, it feels like if I either press down or slide any harder, the Woodstock will be crushed.


There are no springs to pop out. They are part of the battery pack and simply maintain a good electrical connection between the battery terminals and the calculator contacts. When sliding it forward to unhook it at the bottom, push down a bit and the bottom of the battery pack near the feet should pop up. Then just flip the calculator over, and the battery pack will fall out into your hand. When installing the catch at the bottom will simply snap in place. You may have a rebuilt battery back that doesn't fit properly in the calculator.

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