Thanks to our excellent lab technician Elizabeth. I bought a 3.7v battery to replace the one in my 2nd pacemaker. I previously had replaced the 1.8 inch SSD with a SD card, so knew there was more room in the pacemaker case.
I had hoped to buy a very thin battery which I could slip under the SD card but I couldn’t find one with a higher capacity than 500mAh. Instead I looked for the highest capacity I could get which fit into the same battery space. I found a few 1100mAh batteries but then finally found one which was 1500mAh and the same voltage.
I unfortunately couldn’t didn’t quite get the right size, I was about 1-2mm’s off in height. The only way to make it fit was to remove the brackets which protected the old SSD/HD from the battery. As there was no drive anymore I decided its ok to remove them. With them gone, I could shift the battery over a bit and fit it in.
With some great soldering from Elizabeth, I was able to get everything back in the case and screw the whole thing together.
Looking forward to doing similar with my main pacemaker device, maybe?