Can a 15-amp outlet charge 8 batteries?

Time for a little math. But this will be painless (I promise)! 😎

Hello Mike,

I have a Diesel Pusher with six 6-volt house batteries and two 12-volt chassis batteries.  I’m looking at possible storage facilities and some only have a 15-amp outlet available. Will a 15-amps be enough to keep all 8 batteries properly charged?

Thanks - Eddie B

Dear Eddie,

Let’s do a little quick math to figure this out. A 15-amp outlet can easily supply 80% continuously, so that’s 0.80 x 15 = 12 amperes.

Now 12 amperes at 120 volts is a lot of battery charging current at 12 volts. In fact, it’s around a 10:1 amperage ratio. That 12 amps at 120 volts turns into 120 amps at 12 volts. That’s enough current to completely recharge all of your batteries from 50% to 100% State of Charge in several hours.

Back to your question

But you’re actually interested in just keeping your batteries charged in storage which takes a LOT less amperage. Here’s what I use for keeping multiple batteries charged in storage. You can buy one on Amazon HERE.

It’s a Battery Tender 4-bank battery charger/maintainer with a maximum of 1.25 amperes per bank. That’s 6 amperes total current at 12 volts, which is 0.6 amperes at 120 volts (1:10 current ratio). So this 4-bank charger/maintainer would use less than 1 ampere at 120-volts AC.

What about the 6-volt house batteries?

For best series/parallel battery balancing during storage you could disconnect the parallel links between your 6-volt series battery pairs, creating three 12-volt battery stacks. Then each of your three 12-volt stacks could charged by one of the Battery Tender Banks.

What about the 12-volt chassis batteries?

That’s would be a pair of 12-volt batteries in parallel wired like this.

You can leave them connected in parallel and use the fourth charging bank to charge and maintain those two batteries.

Less than 1 ampere at 120-volts AC

These are probably high current estimates since batteries in storage on a tender / maintainer might need 10mA to 100mA of current at 12 volts to keep them charged. So that’s WAY less than 1 ampere of current at 120 volts.

Let’s play safe out there… Mike

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