Question about Beurer Bm 58

Here is the answer from Beurer: "Yes, you can use it [NiMH rechargeable batteries], but we recommend using batteries with a capacity of at least 1,500 mAh to ensure sufficient operating time."

This may have something to do with the fact that some rechargeable batteries no longer have the same voltage and therefore the measurement results may not be correct.
But I'm not sure. -> Enquire with Beurer. Perhaps they will reply.