Where did you get that idea? It’s actually 45-50 units (I’ve seen both listed), unless something changed. Unfortunately, there’s also 15-20 units dead space that it doesn’t count, so you would need a minimum fill volume of like 65 units, give or take.
It doesn’t hurt to try a lesser volume at the very least. I got the error message once that I didn’t have enough insulin in it (tried to re-prime a used cartridge after a software update). All I had to do was add a few more units to the cartridge and start the load process over again.
Personally, my needs are more than yours. I fill 200 units, which registers as “180+” (since you don’t get a specific number until after the first 10 units have been delivered), and change the cartridge every 3-4 days when the insulin runs out. I tried to do fewer cartridge changes, and do a maximum fill of 300 units every time, but found that process annoying. I didn’t like screwing new tubing onto old tubing, and always seemed to get air trapped in the connection. Or I’d have random spare tubing floating around in my supply kit. It’s much easier IMO to just change cartridge and infusion set at the same time. Given the occasional likelihood to knock an infusion set off, I already have an abundance of cartridges on the shelf. No need to further the imbalance.
Incidentally, I do suck the remaining 20 units or so out of the cartridge when I change, and add it to the next cartridge.