Need 12V 80W for 2hrs at a time

Just use "ready". I don't think EV mode will have any effect. The ICE won't run much if the heater (A/C) is off. Pearl would run it about once every 10 to 20 min. for about 5 min. when I tried this.

 

I am assuming that you cannot plug into some sort of charge maintainer. But if you could, then get a Battery Minder 2/4/8 charger and plug it in on the 8 amp, AGM setting.

If we are talking a Gen II, do not put it in EV mode, as dropping out of EV mode burns a disproportionate amount of fuel to recharge the battery. You are also faced with the car burning ~1kWh (500W @ 2 hours) on its own if you leave it turned on.

Another way of stating your problem is that you need 13 amp-hours. That's a bit risky with the car off, as this is over 1/3 of the battery capacity, almost 1/2 if you have the little non-SKS battery. It also means that the ICE is responsible for recharging it -- an amount of energy comparable to moving the car 1 mile -- AND it would take having the car turned on for several hours to do it.

It is an interesting problem. If it were me, I'd get a dedicated deep cycle battery and charge it at home after each use. Then the only penalty to the ICE is the cost of carrying an extra 30 lbs or so.

 

In Ready mode, the 12V supply really won't be coming from the 12V battery, but instead from the traction battery via the 12V inverter. The ICE must then run occasionally to keep the traction battery above a minimum setpoint, and you must not prevent the ICE from running for this purpose. (The ICE can be locked out, but this can only cause bigger problems.) EV mode or not is not relevant.

You should minimize all other loads so the ICE doesn't have to drive them too. Climate control off (heat and AC are large parasitic loads), headlights off. Unfortunately, the mandatory ignition and control system loads take several hundred watts, so most of the ICE operation will be to support these, not your 80W 12V load.

You are right to avoid Accessory mode. While it should work several times, it should quickly lead to 12V battery failure.

But if this 2 hour load is going to be a regular event, I'd give strong consideration to seilert's suggestion of using a separate deep cycle battery for this purpose.

 

The 12v outlet is not great at supplying more than 4 amps. I have found that the connector gets very hot. Look into a separate 12v fused source with a good connector as well as leaving the car in "Ready" mode (in Park, not neutral) so that the system can manage the battery SOC.

JeffD