I have to remove the sender unit to fit a dip pipe to a
supply a cooker/heater.
Supplied instructions are clear but include a WARNING that after disconnecting I only have a *MAXIMUM OF 10 MINUTES* to complete the task and reconnect, before the sender would need recalibration.
Is this true?
Why?
Would I avoid this problem by disconnecting the battery? (which I would do as agood practice anyway).

I just found this information which is relevant (I think?) but it doesn't answer my question about 10 minute maximum disconnection warning.

Quote....

Remove the cover that is part of the floor matting and is between the front seats. You should be able to see an electrical connection. Leave the fuel pipes alone. I have not done this myself yet, so cannot tell you how the electrical plug on the pump is attached; it might be a 'lift the tab' or a 'squeeze from the sides' or some other, but you should be able to figure out how to remove it without breaking it! Before you remove the plug, switch the ignition on. You will hear the pump running (priming the fuel system). Wait about 20 seconds until this sound has stopped (which it will if you do not start the engine) and disconnect the plug. Switch the ignition off. Reconnect the plug and then switch the ignition on again.*

I would hope that you will now see a correct reading on the fuel level guage. If you don't, I am afraid that you will need a new sender after all. It is definitely worth a try though.*

Also remember that if you are going to have a new sender/pump fitted you should make sure that there is no more than half a tank of diesel present, or it will get very messy indeed.

End quote.