NY wrote on 07/02/2019 :

Is there a problem with replacing them with batteries that can hold more
charge ie 750 mAhr. I presume the phone will still charge them at its
standard rate (though it may take longer to charge them).

Go for the largest capacity you can find, but be wary that some sellers
claim a larger capacity than actual. I just bought cheap ebay cells and
they have been fine for the past couple of years.


I will go for branded (eg Duracell) rechargeable batteries.

I presume that if the original batteries are NiMH, I should go for that same
technology.

Yes, the different type have differing charging requirements.