OmegaOmega, I agree with both you and ag4ever. The other devices in use would slowly deplete the 12-V battery. But it's continuously monitored and recharged by the NiMH battery. The ICE kicks in when the ECU decides that the NiMH battery needs topping up. My ScanGaugeII can show the 12-V battery's voltage. As soon as you switch to READY, it jumps from ~12 V to over 14 V. This likely means that in READY mode the dc-to-dc converter is probably supplying all the needed current to satisfy the load on the 12-V battery. In ACC or ON modes, however, the 12-V battery is on its own.

Stan