How long to idle truck to charge truck batteries?

I'd say you're looking at a minimum of 10 minutes just to recharge what you lose from starting the truck. Probably another 10-15 to put some charge back into them.

 

They won't hurt or drain your batteries a phone or a laptop at all. If you're idling your truck make sure you bump your rpms up to 1k. That's more important for the life of the engine.

 

30 minutes

 

Just for reference I run a twelve volt electric fan and charge my phone and I pad on my ten hour brake with out the engine running.
My truck has three batteries and it starts with out even a hint of hesitation in the morning when my brake is over.
If your batteries are in good condition and that’s all your charging you should be good for ten hours no problem with out the engine running.

 

I have to start mine. I got a portable 12 volt compressor for blowing up my significant inflatable other, it kind of takes the batteries down a little bit.
I've tried blowing her up off the engine compressor but she smells like oil if I go that route. Anyways once she is fully inflated it takes about 30 minutes to get the batteries charge back up decent.

Lol

 

I drive my vehicle once every three months or so for a few miles.

In between I give her a run of about 30 minutes. Battery is charged long before then. But it's a chance to not let it get seized up. I usually raise the RPM to keep the carbon buildup out of the engine. A couple miles on the highway takes care of that.

Truck batteries are pretty strong, 3 or 4 of them feeding a cell phone wont matter for years.

 

Watch your gauge, when it’s back up to normal, you’re good, likewise chech the gauge to see if they’re getting low. I run radio and charge phone all night, only 3 old batteries, no problem.

 

I say the best charge is a good 30 minutes. If the truck has many accessories logbook, phone chargers laptops, fridge and inverters. The voltage that you see on the gauge is usually what the alternator is putting out, not your overall battery voltage. Keep on trucking guys.

 

Flooded batteries can show a surface charge, showing full voltage long before they are fully charged.

What you see on the gage when the engine is running is not representative of the charge level of the batteries.

Flooded batteries are not fully charged until they have a " deep charge. "

There's a lot of good info on this topic to be found in the solar power online community, as they use mostly flooded batteries also.