Tennokoe Bank battery replacement?

The Tennokoe Bank uses a battery to keep it's saves doesn't it? Is this possible to replace? Hu Cards don't have screws in them, where is the battery being kept?

 

Apparently there is a CR2320 battery with spot welded tabs underneath the bulge. See link. It look like the cover is held in place with heavy duty double-sided tapes. I haven't tried this, but it look like hair dryer should be used to soften the adhesive first, otherwise the cover will be gouged. It look like a good project for custom cover...

 

Oh is that where it's hiding? Any suggestions on what to replace the battery with? For carts, I use a battery holder, which fits great, but I don't think there would be enough room for one of these. They do have batteries with the spot-welded tabs on the internet, but the batteries always seem to be generic, no idea what their quality would be like.

 

I did a little bit of research on this subject not long ago, but I haven't tried it. I need to get another spare Tennokoe card before I attempt this. It seems most people who replaced the battery end up with a cover that does not seal back flush. It seem like it's due to a combination of using a thicker battery, amount of soldering, wire, or adhesive used. I'm thinking of making a 3D printed spacer that goes between the HuCard and the cover to allow a battery holder or two to be solder in. It will look bulkier but hopefully it will still match the look. It might be a fun project to take on, although I'm not sure sure how practical this will be. I mean how often does one need to swap out the battery...

 

Assuming you can get a replacement battery that not any bulkier than the original, I think this lack of flushness would be down to a thicker adhesive being used (the original looks to be nothing more than a thin adhesive film) or the cover being warped during the opening attempt. If you use something like 3M adhesive (the thin adhesive film often used to stick phone screens down) that would solve the the adhesive issue and if you heated the card from the back (where it's thickest) this would hopefully prevent warping of the cover, provided you don't bend the plastic cover while removing it

 

Soak the side of the card with the battery in isopropanol (rubbing alcohol) for a night and it will likely come loose. The battery is dead anyway and that liquid won't damage the card at all. It should weaken the glue and make it easy to remove.

 

That's a good idea, though the battery isn't completely dead. It still has a charge, but I want to replace it before it does die. Might that be a problem?

 

Not at all, as rubbing alcohol should not be conductive.

 

That's what you'd assume anyway :\ Hoping that 99.5% is pure enough to not cause trouble.

 

Rubbing alcohol is NOT pure isopropyl alcohol. It's more like 70%. It contains water and will leave water when it evaporates. I'd never use rubbing alcohol on a live circuit. And you don't really want to be leaving something soaking in isopropyl alcohol overnight indoors - read the safety sheet. I had to evacuate a basement once because of fumes given off when soaking something in isopropyl alcohol.

Heat would most likely be your best method.

 

At 3v for so little time, no it won't damage anything. Heat will damage the plastic a lot more.

 

I decided to crack open my Tennokoe Bank just to check the voltage. It's actually not that hard to open. It took me less than 5 minutes. I used a hairdryer on high setting and a metal spudger. Start the spudger at the black region of the card as there is is no tongue and groove joint at that area. Heat the area for few moment without lingering at the same spot too long. Pry a little and and resume heating as you get further, before long the cover will come off. The adhesive on the double-sided tape is quite gummy. You can see the residue on my metal spudger. My card still has 3.19V, if I'm not mistaken most new battery measure 3.25~3.30V. I guess there is no point in swapping this particular one out, right?

 

Lithium batteries start to drop voltage only when they're very close to the end of their useful life.

 

I was looking at a CR230 spec sheet, it shows a graph for typical discharge characteristic rate. It shows the voltage will drop drastically once it surpasses 450+ service hours. Granted that's tested at a specific load, but this card should be over 20+ years old at this point, why is the voltage still this high?

 

Because, for these batteries there are at least two grades. The batteries sold at shops for replacement will follow the spec sheet you're looking at. The ones manufacturers put on these devices account for a much longer shelf life as these are supposed to last from 2 to 3 years on a shelf before they're actually used. Add that to the fact that PC-Engine stuff used the highest grade of low power chips that were available at the time and that NEC never used Chinese parts (I don't think high tech stuff with low quality even existed back then... now the market is flooded with low quality stuff and fakes) so the power the thing consumes must be very, very low.

But the chemicals inside of the battery have their actual self degradation rate. So even if the ram doesn't draw enough juice from the cell to wear it out, the time will eventually.

 

Thanks for the explanation. By the way, does the ram draw less juice if there there is no save files? Or it doesn't matter at all.

 

Nice work! Is the plastic on the cover quite thick? I figured it would be really thin and would easily warp due to heat, but your photos makes it look quite thick and solid. How much room is in there? Do you think a CR2032 in a small holder would fit in there? From the looks of your photos, some 3M adhesive would do the job perfectly to replace the original adhesive.

 

The plastic cover is 1.5mm thick, but at the center where there is a recess spot for the battery, the thickness steps down to 1.0mm. I don't think you will warp it by using hairdryer. Heat gun perhaps. Cracking it is more probable from hasten prying. The small slot at the middle of the edge of the card is a misleading area to pry. It seems like an obvious spot to stick a screw driver in there but you'll likely gouge the card first before making any progress. As for roominess, none, the battery stick out about 0.4mm above the card. The cover is recessed enough to accommodate that and the spot welded tab. As for the adhesive, there's no way to reuse the original for sure (at least in my case). I had to use Goo Gone to remove mine. 3M spray adhesive is probably a good alternative if you want your cover to close flush. I'm not sure how easily that can be open in the future though. Since I have mine open, I'm definitely going to design a spacer for this.

 

Hmmmm, looks like I've got no choice but to use one of those batteries with the tabs spot welded to them. Rather than using the spray adhesive, I was thinking more along the lines of those double-sided stickers that you can buy to use in phone repair . They looks exactly like what I can see in your photo.

 

Just mentioning, the hole on the top of the card is to allow for the fumes/gas from the battery to exit the card.