Texas Calculator Battery
Muredac Ford
About replacing the button cell battery on a BA II Plus Financial calculator that does not have a removable battery door:
For safety purposes and to prevent ingestion, the button-cell batteries in school- and student-owned calculators without battery doors are not designed to be replaced. It is possible to replace the battery by removing the back case of the calculator, but opening the back of the calculator voids the one-year, limited warranty. In general, removing the back of a calculator must be done carefully, as TI is not responsible for any damage caused when you attempt to replace the battery. However, since your calculator is already out of warranty, you might choose to attempt to remove the back case to replace the battery. Please let the customer know TI is not responsible for any damage caused when they attempt to replace the battery.
1) Turn off the calculator and place it face down.
2) Using a small Phillips screwdriver, remove the screws from the back case and put them in a safe place.
3) Carefully pry apart the back case and the front case. Be careful not to damage any internal parts.
4) Remove the screws from the metal battery cover and lift it off the battery.
5) Tip the calculator slightly to remove the battery.
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Whether the battery lasts or not is a different question. The question is what if the battery dies ? Are you ready to spend another 6/12 months to preparing for exam just because you could not do pass because your calculator was dead!!? Nobody will be lending their calculator during exam for sure. For Level-1, people might still get through, but for other 2 it is impossible to clear without extensive use of calculator. I think its kind of insurance for your exam ?
Also wondering: are we allowed to bring another non-financial calculator? I would be happy to bring along my scientific calculator (also Texas instruments) because you can see everything you typed (unlike the BA II which only shows the number u JUST typed and that is so annoying!!!!!!).
@RaviVooda: I have used the same calculator in L1, L2 and L3 all trough the exam and the practise. No way it would die just about in L2 unless you use an old one. But no harm carrying extra calcs if that gives u peace of mind like @MattyJ
Texas Instruments' Graphing Calculators have evolved over the years to be rechargeable and have a backlit screen. With these feature improvements, regular AAA batteries were no longer going to cut it. TI switched to using rechargeable lithium-ion batteries.
The battery with the wire was released along with the Ti-Nspire CX, the Ti-Nspire CX CAS, and the Ti-84 Plus C Silver Edition in the early 2010s. We made a nifty little timeline that you can look at below to help illustrate this.
In the first half of 2015, the Ti-84 Plus C Silver Edition was discontinued and the Ti-84 Plus CE was announced. The Ti-84 Plus CE was the first TI handheld released to exclusively use the newer battery design (without the wire).
Half of the Ti-Nspire CX CAS use the rechargeable battery with the wire, and half use the rechargeable battery without the wire. Use the image below to help identify which battery your calculator uses.
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This is my attempt at a LiPo-based battery pack for Texas Instruments Calculators that use the BP01 battery pack, specifically the TI-58, TI-58C, and TI-59. I thought it would be fun to design a 3D printed housing and re-use the circuitry from my rechargeable HP LiPo battery pack. This is a follow-on project to my Classic HP Calculator LiPo battery pack.
LiPo chemistry has very specific care-and-feeding when it comes to recharging, the original TI AC adapter and built-in charging circuitry will not suffice. For this reason, I include a USB receptacle, which allows for charging when removed from the calculator.
The basic idea is to use a gold-flashed (ENIG) PCB as the contact substrate, and mount the LiPo, USB micro B receptacle, and charging circuitry on the opposite side. A charging LED is placed on the same side as the contact pads, but in areas where there will be no mechanical interference. A 3D printed plastic holder ties it all together, and mates with the TI calculator case.
By far this was the most challenging part of this project. I have several original TI BP01 battery packs, so I was able to carefully measure them and create a 3D model using OpenSCAD. This is essentially a 3D solid 'programming language' which (for me) is much easier to work with than an interactive 3D CAD program. It took several iterations to arrive at a working holder design that would 3D print (FDM) reliably. Note that the holder is best printed "flat side down", but that this orientation is not ideal for the retention tab; it wants to break along the FDM layers. I have had good luck with PLA+ material, and even better results with PTEG. Care when inserting and removing is still recommended, however - these 3D holders are nowhere near as strong as their injection-molded predecessors!
The PCB holds the USB micro B connector, the charging circuitry, the protection circuitry, a connector for the LiPo battery, and most importantly the pads that mate with the contacts in the calculator. The overall size of the PCB is 53mm x 28mm. The material is 1.6mm thick FR4. So that the contact pads do not tarnish over time, I chose a gold-flash treatment (ENIG).
Pretty self-explanatory. I used 0805 size components to allow for easy hand-soldering. Note that D1 (LED) and Z1 (Zener) are both polarized, so pay attention to that. Soldering the USB connector requires a fine-tip iron and some patience, or a hot-air solder station. I use the latter with very good results.
Connect the battery to the PCB, double-checking that the polarity of the LiPo is matching the "+" and "-" marks on the PCB. Place the battery into the holder in between the two pairs of screw bosses, and then press the PCB into place above it. Four #2 self-tapping stainless steel screws secure the PCB into the 3D printed holder.
Connect a micro-B cable to the board and charge the LiPo battery. The LED will stay lit during the charging process, and extinguish when it is completed. The charge current is about 220mA (0.2C for a 1200mAhr battery). You can adjust R1 to change the current (decrease R1 will increase charging current) if you need to. It took about three hours to charge my battery.
Install the pack into the calculator. Be very careful with the delicate latch retention tab when inserting and removing the holder, because it is fragile and prone to breakage. If it does break, you can usually re-attach the tab with Krazy Glue. Enjoy using your vintage TI programmable calculator!
I've been enjoying using my TI-58 and TI-59 calculators, and the vastly increased run time before recharging is required. The only drawback is that I have to be very careful when removing or inserting the pack to avoid breaking the fragile retention tab on the FDM 3D printed housing. The reason for this fragility is that the best orientation to print the housing is exactly the wrong orientation to print a robust flexible retention tab.
I then printed several of these, with varying beam thicknesses (0.5mm, 0.6mm, 0.7mm, 0.8mm) from PLA+ which results in a bit nicer overall finish. This orientation puts the axis of bending around the Z axis, which is exactly how a FDM item should be oriented to survive bending cycles. The amount of flex of the 0.6mm beam variant seemed pretty good, so the next step was merely to adapt the rest of the holder model to accept the large "stub" of the tab and try it out:
Of course, when slicing this model, supports are required to hold up the 'bridge' of the socket. It actually took a couple of tries to get the socket part to be strong enough and have sufficient clearance to mate with the retention tab piece. After printing, I carefully cleaned the support stuff from the inside of the socket and inserted the tab piece. The results seem to be much more robust and I feel much more confident about the longevity of this holder versus the less complicated all-in-one style.
Printing the holder from PETG makes a world of difference! This material has a lot more 'give' than PLA and the fragile retention tab really benefits from this. I've even had a few holders fabricated through the Voodoo Manufacturing service and they are even better than what my modest 3D printer can generate - at a very reasonable price (about $6 each holder).
Still playing with the holder 3D model. I had to adjust the latch tab (again) a bit, to correctly engage with the inside of the calculator. I still struggle with the fact that I'm printing the holder "wrong". That is, I'm printing the outside surface of the holder as the bottom, and building upwards - this makes perfect sense for everything except the latch. The latch wants to be printed "sideways" so that the FDM lines are running perpendicular to the arc of motion. Unfortunately, on my printer, this would require a lot of support material and probably result in a really ugly holder.
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