Bosch 18V batteries

Do you mean 3Ah? 30Ah would be car battery sized.

Are they the same as their tool batteries? In which case I'd just buy another, it'll be cheaper than the cells:

Theo

Sorry Theo. Forgot the *.*

Domestic staff waving the machine around my feet currently.

Symptoms, seem to hold charge for an hour or so only. Charger out of sight so they are often left on charge!

Huge price difference between 3.0Ah and the higher capacity versions:-(

My uninformed theory is that keeping them on charge does shorten the life. My Dyson lasted about 20 years with just top-ups. Regular reports of the same model's battery failing within a few years elsewhere.

I tried an 18V 5Ah generic Makita battery on ebay - about a quarter of the genuine price.

Seems fine so far, certainly similar to the genuine equivalent.

At the moment it's powering the Dyson using an Aliexpress converter (thanks Theo) - order of magnitude longer lasting. But then the Dyson was probably losing capacity over some years.