EFIDynoTuning Forum

I'm thinking a 12v nominal car battery discharged down to 10.5 volts is going to take about 230-340ma minimum draw to charge if no load is placed on it. I have approx 10 batteries I'm going to be putting in a battery rack and tossing in the back of my work truck. I drive 2 hours each day so its plenty sufficient to maintain them. Using my worse case of 3.4 amps I'm assuming a 5 amp fuse should be more than sufficient.

I plan on using a spare trailer wiring connector I have so I can easily plug in the battery pack and let it trickle on my excursions. I figured a 5amp diode would be able to survive. Suppose we shall see.

Anyone have a more realistic number or done something like this before with any experiences?

well diode not needed my work truck - 2019 F-150 completely isolates the trailer circuit from the parking lamp circuit so it doesnt backfeed. I've had 9 batteries hooked for the past few days and all has been well.

When I first read this post, I thought "WTF?"
I am assuming you have the 9 batteries hooked in parallel.
I am assuming all batteries are identical, same amp hours, etc.
In a perfect world, each battery would have the exact same voltage, same electrolyte, same age, and take the exact same charge

When a battery with a higher voltage is connected to a battery with a lower voltage, one battery will charge the other.
This process will continue, while draining each battery.

This 'auto-equalization' of each battery is what is going to cause you issues.

The results are unpredictable.
You may have created a 9-cell electro-hydrogen bomb in the back of your truck!

I am also curious as what the reason is behind wanting to do something like this, what is the need for 10 extra batteries? lol

correct
no
these are all different

yes im aware of the nominal voltage

As long as they all get up over 12 volts when charged i.e. no dead batteries then I don't see any issues. Yeah a dead battery would kill the others no doubt.

lol nah no worries..

I have too many vehicles that I don't drive often enough so Instead of rotating charges every so often its easier to maintain them by having them get a little juice each day to keep them topped off. I calculated out 136 hrs of engine run time with the alternator giving them 13+ volts. I'm thinking that would be better than using a charger to charge them every other month or so.

These also act as my backup inverter power backup when the electricity goes out during hurricanes and such.