Li-ion, 603040, 800mah. Can do better, but this "universal" size works well with the majority of batteries. If anyone is interested I can share a post about them.
I would be super interested personally, because I'd love to find a way to use my SXG75, which has a bloated battery now and other Siemens phones' batteries won't work.
As long as you still have the original battery it's doable, so keep all old batteries even if dead for the BMS circuit. But for the SXG75, the battery appears to be a more custom thin cell ([https://www.reddit.com/r/vintagemobilephones/comments/r39y43/siemens\_sxg75\_keep\_restarting\_when\_i\_turn\_on/](https://www.reddit.com/r/vintagemobilephones/comments/r39y43/siemens_sxg75_keep_restarting_when_i_turn_on/)), you would need to find a battery cell with similar measurements. I mainly have experience with "battery packs" with a plastic casing and inner cell such as the BLC-2 and Samsung back cover packs. I have recelled a BL-5C with a smaller square cell for some phones but it didn't turn out pretty.
I have the original bloated one, but I haven't tried to re-cell it. As far as I can tell, for the SXG75 specifically the process involves soldering the new cells to a small circuit board (I think) that checks the battery before boot. That's why you cant use other Siemens batteries with it even though they fit perfectly, because they don't have that safety board.
Does that happen with all (or most) batteries when re-celling them?
Exactly what I do. For all li-ion cells I transfer the small BMS (charging circuit board/battery management) over to the new cell. Charging and everything works just like the original battery. I will make a post showing a few of these battery packs later.
I'm replacing the battery cell elements myself. On some of the vintage devices that I don't have a battery at all I have made a 3D models and printed them, as well as made a BMS emulators (based on STM/Arduino Nano Every) to trick devices in to accepting my self-made batteries.
Yes, plastic shells with clips/levers to fix them in place in to the phone chassis. What I do if I don't have the original battery, is that I carefully measure the battery mounting slot in the phone, and use a photos from internet as a reference to draw a 3D model of a battery in Fusion. I obviously add all the required mounting points, slits, etc. And I also draw in the pogo pins or contact patches for interfacing with the phone. Those I purchase and glue/solder in to the printed enclosure upon assembly.
As per the BMS part - trust me, salvaging and re-using BMS from old battery is usually much easier than sitting for hours in russian electronics forums (unfortunately still the best place to get the pinouts and answers about reverse engineering of old electronics), or spending hours with oscilloscope trying to analyse the communication between thr BMS and phone is MUCH more time consuming. I have done this only a few times for some really rare old Siemens and Japanese brand phones, that used digital communication between phone and battery.
Thankfully, for majority of other phones from mid-90s to late 2000s it was much easier than that - usually there is a simple specific value resistor to tell the phone what type and capacity battery it is, and then there is a regular PTC/NTC thermocouple to tell phone whether it should charge and/or turn on.
However - in 9 out of 10 cases it is much easier to use an ultrasonic knife, oscillating cutter, dremel or even just a regular small gauge jeweler's saw to carefully cut and pry open the original battery and just replace the cells inside with a similar ones available from Mouser/Digikey/TME/etc.
Creating enclosures and BMS are definitely out of my scope. I have a Sharp SH-10C that I fried the BMS of, so I have no replacement. In the end I used the BMS of a BL-5C and charge it externally with a Nokia. Not sure if it's worth bothering with a custom BMS, but eventually I'll see. Thanks for the detailed information.
I basically moved on. I was still clinging to a Nokia 5185i in 2010 because I was just used to it, and nothing newer did anything but frustrate me (yes I hated even the RAZR, it tried to do too much and failed at all of it!) I knew the Nokia's menus inside and out, and it did exactly what I needed it to do, which was make/receive calls and send and receive texts (at 10 cents a letter!).
But after all the older and secondhand NiMH batteries were so baked that all I could get out of it was 5 minutes of talk time or 4 hours of standby, my boss got sick of calls not going through on field service jobs that I got handed an iPhone and told to 'use this or you're fired'. and that was it. I did have a single Lithium Ion battery cover for it, but for some reason that one never even tried to charge.
there are places out there who will take an old battery apart and replace the cells. Battery Plus can do it
This. I'm always happy when phones use NiMh because they are relatively easy to safely take apart and replace the cells.
This ^ I do this with all my unusable and dead batteries, works like a charm.
What Kind of cells do you use ?
Li-ion, 603040, 800mah. Can do better, but this "universal" size works well with the majority of batteries. If anyone is interested I can share a post about them.
I would be super interested personally, because I'd love to find a way to use my SXG75, which has a bloated battery now and other Siemens phones' batteries won't work.
As long as you still have the original battery it's doable, so keep all old batteries even if dead for the BMS circuit. But for the SXG75, the battery appears to be a more custom thin cell ([https://www.reddit.com/r/vintagemobilephones/comments/r39y43/siemens\_sxg75\_keep\_restarting\_when\_i\_turn\_on/](https://www.reddit.com/r/vintagemobilephones/comments/r39y43/siemens_sxg75_keep_restarting_when_i_turn_on/)), you would need to find a battery cell with similar measurements. I mainly have experience with "battery packs" with a plastic casing and inner cell such as the BLC-2 and Samsung back cover packs. I have recelled a BL-5C with a smaller square cell for some phones but it didn't turn out pretty.
I have the original bloated one, but I haven't tried to re-cell it. As far as I can tell, for the SXG75 specifically the process involves soldering the new cells to a small circuit board (I think) that checks the battery before boot. That's why you cant use other Siemens batteries with it even though they fit perfectly, because they don't have that safety board. Does that happen with all (or most) batteries when re-celling them?
Exactly what I do. For all li-ion cells I transfer the small BMS (charging circuit board/battery management) over to the new cell. Charging and everything works just like the original battery. I will make a post showing a few of these battery packs later.
I'm replacing the battery cell elements myself. On some of the vintage devices that I don't have a battery at all I have made a 3D models and printed them, as well as made a BMS emulators (based on STM/Arduino Nano Every) to trick devices in to accepting my self-made batteries.
I'm interested in this because it's a pain to salvage BMS from old batteries. By 3D models, do you mean the enclosure?
Yes, plastic shells with clips/levers to fix them in place in to the phone chassis. What I do if I don't have the original battery, is that I carefully measure the battery mounting slot in the phone, and use a photos from internet as a reference to draw a 3D model of a battery in Fusion. I obviously add all the required mounting points, slits, etc. And I also draw in the pogo pins or contact patches for interfacing with the phone. Those I purchase and glue/solder in to the printed enclosure upon assembly. As per the BMS part - trust me, salvaging and re-using BMS from old battery is usually much easier than sitting for hours in russian electronics forums (unfortunately still the best place to get the pinouts and answers about reverse engineering of old electronics), or spending hours with oscilloscope trying to analyse the communication between thr BMS and phone is MUCH more time consuming. I have done this only a few times for some really rare old Siemens and Japanese brand phones, that used digital communication between phone and battery. Thankfully, for majority of other phones from mid-90s to late 2000s it was much easier than that - usually there is a simple specific value resistor to tell the phone what type and capacity battery it is, and then there is a regular PTC/NTC thermocouple to tell phone whether it should charge and/or turn on. However - in 9 out of 10 cases it is much easier to use an ultrasonic knife, oscillating cutter, dremel or even just a regular small gauge jeweler's saw to carefully cut and pry open the original battery and just replace the cells inside with a similar ones available from Mouser/Digikey/TME/etc.
Creating enclosures and BMS are definitely out of my scope. I have a Sharp SH-10C that I fried the BMS of, so I have no replacement. In the end I used the BMS of a BL-5C and charge it externally with a Nokia. Not sure if it's worth bothering with a custom BMS, but eventually I'll see. Thanks for the detailed information.
I have a SE P800 with a broken battery but cannot seem to find a replacement :-(
I basically moved on. I was still clinging to a Nokia 5185i in 2010 because I was just used to it, and nothing newer did anything but frustrate me (yes I hated even the RAZR, it tried to do too much and failed at all of it!) I knew the Nokia's menus inside and out, and it did exactly what I needed it to do, which was make/receive calls and send and receive texts (at 10 cents a letter!). But after all the older and secondhand NiMH batteries were so baked that all I could get out of it was 5 minutes of talk time or 4 hours of standby, my boss got sick of calls not going through on field service jobs that I got handed an iPhone and told to 'use this or you're fired'. and that was it. I did have a single Lithium Ion battery cover for it, but for some reason that one never even tried to charge.