I have a Wren 54, and I notice from the instructions that they recommend not using a NI-MH battery for the ECU. Any ideas why, I have used one for a few flights with no problems.
John

I think it has to do with the ability to deliver high enough current to the starter motor.
Think modern NIMH cells are no longer limited. I'm using a NIMH GP3300 based battery in my Simjet 2300 with no problem.