FT-60R Battery Pack

[VK2CSW]

Recently the Ni-MH battery pack for my FT-60R has decided to show signs that it is on it's way out.  It's 6 or 7 years old so I am not too unhappy.

I have a AA battery pack lying around so I decided to put it to use.

I filled it with alkaline AA's and the FT-60R sprang to life.

Now I have a couple of AA sized lithium 3.6v (primary) batteries that are surplus to requirements.  3.6 + 3.6 = 7.2v - it adds up!

If you look at the attached image you can see I have inserted them into the battery pack and the black jumper bypasses the missing battery slots.  At the terminals I get 7.3v.  Seems good.

When I load it into the radio nothing happens.

So I took out the lithiums and put the alkalines back in. I then used the green and yellow jumpers to attach the battery pack to the terminals in the radio and, as expected, the radio worked.

I removed the alkalines and refitted the lithiums and the black jumper.  Attached the green and yellow jumpers to the radio terminal - nothing.

I then connected the green and yellow jumpers to a small LED board which lit up merrily. So the batteries work, the case works, the radio works it's just that the batteries, case and radio won't work together.

Could the FT-60R be looking at the power source and deciding that the internal resistance (or something) of the batteries is out of spec and goes into protection mode or something?

I mean it's not a hard thing - some batteries, a case, some wire and a radio, what could I be missing?