12 v Battery Box with Charger & Battery Booster

April 8, 2016

I wanted to build a fully integrated, portable, 12 V battery box for portable operations like Field Day.  When I found these Ridgid cases at Home Depot, I thought they were a convenient size, well built, looked great and were a reasonable price.  I also noticed there are clips on the sides that allows you to stack the boxes and lock them in place.  It occurred to me that I could build up a set of modular radio cases and easily stack them up and snap them together.  One case for the radio, one for power, another for accessories or whatever.  A lot of Go Kits include radios, accessories and batteries all in one case, like a 19″ rack case.  While these look great when they are set up, the big problem is weight and bulk.  They are very heavy and hard to move around.  I prefer to have smaller cases that are easy to carry and also provide of some degree of modularity.  If you want a different radio, for example, you can still use the same battery box.

ridgidcase     Ridgid stacking lock

Having one box with the battery system on the bottom and the radio in a second box on top makes for a very neat, modular, installation and it’s not going to move around or fall over in transit.  Perfect for loading into the back of the SUV !

Another really handy feature is a row of recessed spaces about 1″ square.  This helps make the box’s structure more sturdy and I realized these little 1″ recesses would make a great place to put connectors, switches and LED because they would be recessed to avoid damage and accidental activation.

What’s inside

The battery box is a full battery system based on a 35 Ah SLA battery.  While I am a big fan of LiFePo4 batteries, the SLA’s are fairly forgiving and inexpensive.  In addition to the battery, the system includes an AC charger, fuse, low voltage disconnect, power control latching relay, battery booster, solar charge controller, power pole connectors, power status LED and on/off push buttons.

Schematic diagram

12v case schematic

Inside view

12v case top     12v case top 2

In the left compartment is a smart, multi-stage, Genius 7 amp AC battery charger.  When going to the field, the night before I want to open the case, plug in the charger, and make sure everything is ready to go the next day.  The charger is screwed to the base of the case.  Having everything in the case means you don’t have to rummage around to find that charger you misplaced.  While there are smaller, cheaper chargers, the larger charger will charge the battery faster and also charge other, bigger deep cycle batteries as needed.  I clipped off the charge lead connector and replaced it with a power pole.

Genius battery charger

genius charger

The center compartment has the 35 Ah battery in the back.  There are two #8 screws and a bracket that hold the battery in place.  In front of the battery is the fuse, power control relay, and low voltage disconnect.

Power control relay

The power control relay is a 30 A rated latching relay.  Putting 12 volts across the two relay control pins will snap the relay open or closed.  It is very important to be able to fully disconnect the battery from all loads.  If you leave the battery connected full time to the LVD, solar charger, etc, they each draw a little current, even when off.  If you leave the battery unused for several weeks, these little loads will slowly drain the battery so a full power disconnect is important.  I use the latching relay because I can remotely actuate it from the push buttons on the side of the case without opening the case.  Latching relays themselves only take power when switching so when the relay is on or off it draws no current.  They are more expensive but well worth it.  I just wired up directly to the terminals and wrapped the relay in electrical tape then ziptied it down to a screw mounted in the bottom of the case.

West Mountain PWRgard Low Voltage Disconnect – LVD

west mountain lvd

The low voltage disconnect (LVD) is a WestMountain device that shuts off the connection to the battery when the voltage drops to about 11 volts.  This is very important so you don’t over discharge the battery and damage the cells.

TGE battery booster

tge battery booster


The right compartment contains the battery booster and solar charge controller.  The battery booster can be switched on and off.  It takes the battery voltage and steps it up to 13.8 VDC and the output is connected to an Anderson power pole connector on the side of the case.  These boosters do a great job.  They are low noise and fairly efficient.  They are rated for 90% efficiency.  If you don’t want to take the hit, you can flip a switch on the booster and turn it off.  I will just pass the 12 VDC from the battery to the external connection.


Genasun solar charge controller

ganasun solar charge controller

The other Anderson power pole connection is for a solar panel input.  That jack is wired to a Genisun 10A MPPT solar charge controller designed for SLA batteries.  These chargers have a good reputation for being low noise chargers.


Side view

12v case side     12v case buttons

The side of the case has the green power LED that comes on when the power is turned on.  The green push button connects the battery to the rest of the power system and the red button turn the power off.  The dual Anderson power pole connectors are at the back of the case side.  One connector for 12 VDC out to the load and one for the solar panel input.


Shopping list

Ridgid case

35 Ah SLA battery

Genius 7A AC charger

Panasonic Latching relay

West Mountain low voltage disconnect

TGE battery booster

Genasun MPPT solar charge controller

Powerpole connector