How To Build A Backup Battery System
circuit breaker
Safety first, a 100 amp circuit breaker is a great addition. It’s more expensive than a simple fuse but easier in the long run. Electrical tape on the ends adds to the security. Your local auto parts store will have a range of cables in sizes and gauges that are appropriate for your project. Do not skimp on the cable – get the proper rated size for your application.

We have already talked about the inverter and that there are modified wave inverters and pure sine wave inverters. If all you require is something to power your small air compressor then get the least expensive option. If you are going to be running your laptop or desktop computer with it, or medical equipment like us, then you want the more expensive pure sine wave inverter. Then you need to consider the output required. A 300-watt inverter will power basic small equipment but do not even think about trying to plug in your toaster or full-size drip coffee maker. Before investing in your inverter, look at the requirements of the equipment that you want to be able to use. Then consider whether the common sizes of 300, 1000, 2000, or 3000-watt inverters will work for you. Personally, a 300-watt pure sine inverter does the job and we have this hooked up in our RV. This was our first attempt at an inverter and, as the battery array is already in place, it is quite easy. We installed the inverter in a storage compartment (oh, how nice it would have been if this inverter had a wired remote control) and you can plug in right there. We also ran an armored wire along the underside of the RV and then into the living cabin where we set up an outlet. We used a different color of outlet to highlight that this is inverter power and not land power (when the RV is plugged into power at a campground). This 300-watt system is not enough for a toaster or coffee maker, but it is ideal for a laptop computer or charging an iPhone. And it can capably run all of our grandson’s equipment – and that is the prime reason for the inverter.  The second system we set up, as a portable system, uses a 1000 watt pure-sine inverter. Portable is questionable, as the type 27 battery in and of itself is over sixty pounds. A smaller battery will return some level of portability but with an obviously limited power lifespan. We have it mounted in a Rubbermaid tub and soon will be adding a wood base with casters so that it can easily be rolled about in the garage and house.

inverter tray
A wood shelf that sits on ledges built into this tub provides an excellent base upon which to fasten the pure sine wave inverter. We cut this with a jigsaw (using the inverter as the power source) so that we could curve the ends to friction fit inside the tote.
battery tender
The value of a unit like this is only there if the battery is fully charged when you require it. Thus adding a battery trickle charger is simply a wise idea. Notice the Spanish text – this came from
Compact unit
With everything fastened down this unit is ready for reasonable movement. Plug the trickle charger into your house electrical system to keep the battery charged up. Just like your car battery, ensure that all of the positive leads are covered. Or get a solar panel and you can move off the grid – with the small stuff.


  1. Why didn’t you use a lithium ion Car battery for a light weight solution?
    Why not put everything on a movers dolly so you can wheel it around easier?

  2. Why not use an lithium ion car battery instead of the heavy deep cycle battery?
    Couldn’t you put the bin on top of a movers dolly to more easier roll the thing around instead of trying to carry it?

  3. Hi Davin x2,
    Great questions. The idea behind a deep cell battery is that it can handle the repeated draining and charging required in a setting like this. A Group 27 lithium ion battery, similar in capacity to the Group 27 battery used here, would cut the weight in half as they are just under 30 pounds. However, they cost in the neighbourhood of $1000 which is FIVE times the price of the battery used. Our choice was the best price to power ratio.

    A car battery is designed to provide a huge burst of power for a short time and then be recharged by the alternator. Drain it frequently and it’s life will be shortened. A deep cell battery is designed to provide steady current over a long period of time; drained right down without shortening their lifespan. It will not work well to start your engine as it doesn’t have the cranking power.

    The Group 27 is a large and obviously heavy battery and was specifically chosen for the lifespan and amount of ongoing power it would provide at the expense of weight. We knew it wouldn’t be portable. As mentioned in the article on page 3, we will be getting some castors for the case so that it can be rolled about more efficiently.

  4. Hi there,

    You mentioned solar panels. How would one go about hooking this up to solar? My son had SMA and we’d like to take him places next summer. This with solar would be perfect.

  5. Hi Mike, I don’t know a lot about solar power but it appears to me that many solar panels have the ability to charge batteries. I will be looking into this more eventually. Sorry I cannot give you more substantial answers but I just haven’t set this up myself.

  6. Quick crazy Question..
    could i adapt this as a in car solution to not use the existing car battery? how would i charge? i guess plug in the charger to either an alternator or in to a lighter socket? Is this possible?

    1. Hi Jeff, first sorry that I’m over a year late in responding. Second this is not a good idea as it would drain your car battery quickly thus leaving you stranded. There are low power inverter systems you can get that plug into your car lighter socket that would be a better solution – but they will drain the batter if the car is not running.

  7. 2.5 years later.

    Lemme think. A typical larger 12v lead acid deep cycle battery is 100ah (or 1200 wh).

    I think that lead acid batteries can use less of their total rating than a lithium battery (50% vs. 90%? something like that).

    A lithium backup battery setup complete with built-in charging stuff and inverter is something about $1 / wh, so for $500-$600 you could have roughly the same setup but much more portable,etc.

    I’m just not feeling the love here.

      1. Not in the case of lithium all-in-one emergency batteries.

        They’ve been at about $1 / wh all this time. It’s the sort of thing I keep track of living in a state that has regular power shutdowns in order to avoid fires. Gas generators are kind of a pain to listen to.

        I’m actually kind of surprised there haven’t been big price drops, perhaps the technology is currently at a sticking point with these sizes.

        Now, a really brilliant product would be to take an electric start generator, hang a good sized battery on the front of it, and cycle the generator to keep the battery full. That same battery could be used to start the gas motor when needed. All downstream power would be through the battery (and an inverter, a thing that better generators already have). There’s no point in having a gasoline engine roaring the whole time.

      2. as an aside, the best part of plumbing a battery between a gas generator and a power consumer is that the generator could be sized to average load rather than peak.

      3. Just as a data point, I bought a Polaroid PS600 (578wh) for $329 plus tax in October of 2019, and an Audew 220wh unit for $154 in Dec of 2018. Prices tend to jump up and down on these sorts of products.

        If you can build something like that out of a cobbled together lead-acid setup, that would be cool. One advantage of homemade is that the individual pieces are replaceable if something fails plus, if you go big on components, the system is expandable. Pretty soon you are building a whole-house battery backup which is a whole ‘nother thing.

  8. Lots of great ideas, William. For comparison, a PS600 in Canada is $1000 – if you can find one. My hope for the article was to provide some lower cost options for people who needed a short term solution. Sounds like you’ve got ideas for ongoing and long-term solutions! And I’m guessing that if you haven’t gone the whole house route, that this isn’t too far away!

  9. Your design does not include an auto-on for your inverter. It is possible for your inverter to be turned off (unintentionally perhaps) meaning no backup if your system is unattended.

    That remote switch on the Eliminator Inverter most likely has unused pins. Mine has. Two of those non-populated wire on the RJ-11 connector (black wire and white wire can host a fix SPST switch. I build a circuit that monitors the hydro and turns on the inverter is power has gone off. The circuit uses an electronic switch instead. I added a relay to switch the load from main to inverter power with hydro goes off. It returns to original when hydro comes back on. I like your choice of AGM batteries and multi-stage charger.

    1. Hi Ray, that is more complex than I needed but certainly extends the functionality. In my case, we are always present when running the inverter. And as it’s an RV that is usually ‘boondocking’, there’s no electrical connection to shore power when the inverter is in use. Thanks for making me think about possible expansion routes!

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