@mikerj the ultra Z batteries still come down cheaper, i don't mind stripping the protection circuitry that is included in it, plus sony over the generic tablet battery sounds like a better idea.
@amyk
1. i'll definitely check but i suspect they'll be pretty close bought together.
2. I didn't strip the plastic sheath off the battery, as it's probably all the lithium firemaker inside under it, but it just has the contacts coming from the cell, but i suspect ill overcome this hurdle when i come to it, I think i got good odds there being some sort of metal tabs already spot welded between battery and the protection circuit on the cells i'd purchase, so i could solder to those tabs without impacting battery at all.
3. i wont worry about this, it's something the little MP44A is reporting back, since ill keep that, only replacing the cells, it should work perfectly fine and not cause any issues. hopefully.
i think i'll go for ultra z pair of batteries, they come down 5£ a pop, so 10£ all in, same capacity as these, size should fit perfectly too, just slightly thicker, but there is enough room in there. those nokia cells only come form china, i don't think i want to wait a month for them to get here... those generic tablet batteries, i don't think are worth the risk, i've tested a few of the cheapo 1000000mah external usb batteries for charging phones, them cells usually have half of decent ones, at best, not to mention the claimed spec.
edit: got a pair of them ULTRA z batteries, will see where it gets me tomorrow or day after and post an update and maybe the magical journey of soldering 4 contacts and putting on some insulation.