On my heating oil tanks I have 'Watchman' monitors, that radio on an infrequent basis to an indoor receiver to tell me how much oil is left.
I have three separate heating systems in three buildings - they all have Watchman monitors of varying vintages, but all have one thing in common. A 6 volt battery encased in a copper tube entirely proprietary and hugely expensive.
I recently took delivery of a 'top up' of oil (2300 litres and that's a top up
) after which the monitor for my workshop ceased to work. Obvious first thing to look at is the transmitter battery - sure enough it's down to 5 volts off load so change the battery. New genuine battery over £30 !
Now I know from previous investigations that these things consist of a screw connector sealed in the end of a piece of standard 15 mm copper plumbing pipe, which has a cap at the far end, and a plastic sleeve bringing the bore down to the diameter of an AAA battery. Inside are four AAA batteries and a spring to make contact.
So - mount the pipe in the lathe - carefully part it off down to the plastic liner and clean the ends. Then take a 15 mm compression joiner - bore out the centre stop so that the pipe will slide all the way back together, and re-assemble with new batteries and lashings of Vaseline as that is what it seems to have been previously smeared in.
Actually slightly more complicated - I only had a bulk head fitting with no conical ends for the 'olives' so I had to machine them.
Wack it back on the transmitter and wait to see if now it will talk to the receiver. This can take a long time so the fault may or may not be fixed - but the battery is at least now good