Help with BTL power requirements

I have four small power amp modules I built some years ago for a project that I dropped and didn’t complete. I’ve never built a BTL amp before, so I thought these would be good candidates to experiment with. I know the power requirements for them (single module, mono), how do I figure the requirements if I BTL two together. I can’t find anything in any book on my shelf or on the net? HELP! Any suggestions or point me to an article. Thanks.
Let me restate question...

Thanks for the replies, but I think I might not have been clear in my question. I know how much output (theoretical) power should be. What I am trying to find is a formula to figure power supply needs. I know the voltage and current needed for one module (mono, single ended), how much is needed for two modules in BTL, that is the formula I haven’t been able to find. Thanks.

BTL has the same power requirements as the two separate channels
into half the load connected, i.e. for an 8 ohm load it is the same as
for two channels into 4 ohms.

Generally speaking small amplifiers are not good into low impedances
and are therefore not suitable for a BTL amplifier unless the load
impedance is unusually high.