Can you charge two 6 volt batteries with a 12 volt charger

12-15-2016, 07:56 PM

#10

Senior Member

Table of Contents Show

The Sideways Movement Simple Campervan Wiring Diagram Series Part 2
Charging 6 Volt Batteries In Series With 12 Volt Charger
Two 6 Volt Batteries In Series VS One 12 Volt
Reader Interactions
What happens if you use a 12V charger on a 6V battery?
Can you charge two batteries with one charger at the same time?
Can you hook up two batteries to one trickle charger?

Join Date: Dec 2012

Location: Edmonton, Alberta

Trailer: 1979 Boler B1700

Posts: 14,815

Quote:

Originally Posted by Tom and Sharon

I know 2 x 6V = 1 x 12V, but my concern about charging 2 in series would be if somehow they were not equally discharged.

Quote:

Originally Posted by padlin

How could they be not equally discharged?

It is true that two 6-volt batteries in series can get "out of synch", and have different levels of charge. Ideally this shouldn't happen with the batteries in series (so the same charging and discharging current goes through both), but in practice it happens because batteries are not perfect and internally discharge to a small extent. Any battery self-discharges slowly while in storage without any external connection, and each cell is doing this... at slightly different rates; two groups of cells (that is, two batteries) will self-discharge at different rates and so end up mismatched.

Cells - and batteries - in series get out of synch during charging, not just storage. Not all of the charge put into a battery is successfully stored by the battery, and even "identical" batteries won't perfectly match each other in charging efficiency, so they end up with different charge levels. During normal discharging in use the same sort of thing happens.

This isn't a big deal, and exactly the same thing happens between the cells of a battery (whether 6-volt or 12-volt). When a battery dies, it is often just one cell that has gone bad, but since they are all built into one case the whole battery has to be replaced. With two 6-volt batteries, the usual advice (which makes sense to me) is to treat them as if they were attached to each other: buy them as a set, and replace them together with another set.

So, charging the pair of 6-volt batteries together means just treating them as one big 12-volt battery (as others have already posted), and clearly that works.

The question is whether or not there is a meaningful benefit to taking advantage of the opportunity to charge each set of three cells (one 6-volt battery) to the same state of charge and reduce the mismatch.

Quote:

Originally Posted by Tom and Sharon

Since the charger goes through multiple charging phases, how would that work?

It's the same as with any battery made up of multiple cells: the charger sees the total voltage, responds to that total, and the change between charging modes isn't quite at the ideal point for each individual cell. That's okay - even if there were one charger per cell normal chargers still wouldn't manage the charging ideally.

This is the second installment of our Simple Campervan Wiring Diagram Series. In this diagram, we look at using a 6V Battery Bank instead of a single 12V Battery. Below you will find a 6-volt battery bank wiring diagram for charging 6-volt batteries in series with 12-volt charger.

*Electrical work should only be done by a qualified service professional. These diagrams are here for use at your discretion*

The Sideways Movement Simple Campervan Wiring Diagram Series Part 2

Charging 6 Volt Batteries In Series With 12 Volt Charger

If you do or plan to do any type of off-grid camping (boondocking), then a 6V battery bank system is a superior choice over a single 12V battery. A 6V Battery Bank Charging System will give you added amp hours and increased life cycles. By charging 6-volt batteries in series with a 12-volt charger you allow your off-grid electrical the true capacity it needs.

Two 6 Volt Batteries In Series VS One 12 Volt

Life cycles

6 volt AGM Battery has more life cycles. (Discharging down do 80% depth of discharge.) 600-700 on average. A 12v AGM Battery, on average has only 150. Winner: 6V Battery Bank

Cost

The 6 Volt option must be used in groups of two. Because of this, the overall cost of a 6 Volt Battery Bank is much higher than the single 12 Volt option. Winner: 12V Single Battery

Size and Weight

The fact that you will need two batteries wired in series means a larger physical size and more weight than a single 12 Volt battery. You will need to take this into account when planning your build. Winner: 12V Single Battery

Dry Camping and Off-Grid Use

The 6 Volt AGM batteries have larger cells and because of this, they have a higher amp hour rating. A 6 Volt battery Bank I the best option if dry camping or “off the grid. Winner: 6V Battery Bank

Parts Required: (See the bottom of the post for some tips and pointers)

Auxiliary Batteries
Inline Fuse Holder and Fuses
VSR Voltage sensing Relay
Battery Connection Wire
House Fuse Panel

Tips and Pointers

Batteries; AGM type batteries are one of the best options for this situation. They don’t spill or produce dangerous gasses. The capacity of your battery will be dependent on the system load.
Fuses; Be sure to use fuses on all positive wires and install as close to the battery as possible.
VSR; The VSR or Voltage Sensing Relay is very important, this will automatically separate your house battery from the vehicles starting battery. This is needed so when the engine is off, your house systems do not draw power from the start battery.
Wire; The size of the wire you use is dependent on the system capacity. Although you could get away with using a smaller gauge wire, I recommend using the largest possible. This will allow for the quickest possible recharge once you start the engine. It will also prevent the possibility of burning wires.
Grounding; Although you can get away with just grounding the Auxiliary battery. I recommend running a neutral back to the start battery as well as grounding to the chassis at both batteries.

More to Come

Part 1 in our Simple Campervan Wiring Series: Auxiliary Battery Charging System

Check Out Some Of Our Other Posts On Conversion Van Electrical Systems

Installing A Battery Isolator In Our Van
Van LED Lights
Installing 12 Volt Sockets and USB Chargers
DIY Portable Power Station

You, Will, Need A Good Electrical System If You Plan On Adding A Heater Or Roof Vent

Gasoline Van Heater Install
Van Roof Vent Installation

Finally, if you are interested, check out some more #Vanlife related content Here.
And remember, always take the road less traveled!

Reader Interactions

What happens if you use a 12V charger on a 6V battery?

This will run your battery dry and create a thermal runaway scenario, which is very dangerous. Again, some people use a 12V charger to get their 6V battery jump started, but it is never advisable to use a 12V charger to try to fully charge your 6V battery.

Can you charge two batteries with one charger at the same time?

As long as each battery is connected to your charger through the same number of interconnecting leads, and the total length and gauge of these leads is the same, perfectly balanced charging can be achieved.

Can you hook up two batteries to one trickle charger?

9. Two Batteries in Parallel, One Charger. Batteries connected in series strings can also be recharged by a single charger having the same nominal charging voltage output as the nominal battery pack voltage.