Tricky Dicky wrote:

Just had a close look at the meter, there is a battery symbol on the
top with Lithium written inside and a label saying 433MHz, so I am
assuming the battery is rechargeable

More likely a Lithium thionyl chloride primary cell,
10 year D-type used in many smartmeter applications, e.g.

https://uk.rs-online.com/web/p/d-batteries/2019466?