I'm moving into my car and I may need to wire up ventilation that doesn't depend on the engine running. So I found these case fans. However, because I'm not going to be using the car battery, I need a power source. I've been looking at a few power stations such as this one, but nowadays I tend not to trust obscure sellers on Amazon; regardless of the review rating, and even though the price is more than I want to spend it's far less than the going rate for the same specs, which screams to me "to good to be true".
Alternatively, I thought about just using rechargeable D cell batteries. The fan's max draw is 12V at 0.16A. Which is 1.92W each, assuming max load which I am. If I have 4 fans running while I'm sleeping, and let's assume a 10hr sleep, that is 76.8Wh or 6.4Ah at 12V.
I found these rechargeable D cells on Amazon. They're 10Ah each. If I wire up seven of them in parallel that should give me 70Ah at 1.2V or 84Wh; for anyone that knows what the usable percentage of that will be, that would be helpful. So it would appear that with six of these batteries fully charged, I'll have the energy to fully power the fans at full blast all night long. Is this correct? -- assuming they could run at 1.2V, which they can't.
Now, I'm going to have to step them up. And since we're assuming max load, that puts me at 7Ah at 12V. Will stepping it up reduce the energy enough such that I need to add more cells?
And finally, I'd like to be able to charge them while the car is running, transparently, i.e. without having to remove them from the circuit. Can they be both attached to the fan circuit and wired up to be charged simultaneously? Is running the fans off them and charging them at the same time possible?
So to summarize the important questions:
1) Are 7 of these cells enough assuming connecting them in parallel and stepping up the voltage to 12V? 2) Can they be both attached to the fan circuit and a charger at the same time?
That's all I got I think. Any help would be greatly appreciated!