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The two weak points in you initial experiments are going to be the inverter and the battery plant.
- I tried to run an efficient chest freezer on a good-sized portable inverter during a power failure. The inverter's electronic protection circuit immediately tripped out at every attempt. The inverter could easily have RUN the freezer based on Kill-A-Watt readings, but was incapable of STARTING it. Make sure an inverter is chosen with enough surge capacity to start motor-driven appliances if needed, such as a refrigerator or a well pump.
- Mixing and matching reclaimed batteries is a recipe for disappointment. When connecting batteries in parallel, a strong battery will discharge itself trying to "top up" the charge in a weak mate. That's why it is strongly recommended to always replace batteries in matched sets.
Sure, you could test pallets full of discards to find some equivalent batteries to mate, but do you want to spend the rest of your your life nursing batteries? The only upside is that you are getting them for free.
One cheap source for getting working but used deep cycle batteries for stationary use recommended online has been buying big 6-volt pulls from a golf-cart service vendor. I have not investigated this myself.
- Also, lead-acid batteries are not good for some of these applications. Running LED lighting with a steady resistive draw, OK. Please note that most deep-cycle batteries (not starting batteries) are rated at C/20. This means that a 100 amp-hour deep cycle battery should provide 5 amps for 20 hours to depletion. You cannot expect a 100 AH battery to provide 100 amps for 60 minutes.
Also, lead-acid batteries do not "come back" after repeated deep discharges. I looked at one premium manufacturer's graph for deep-cycle recovery, and if discharged to depletion (defined as about 1.75 volts per cell, or 10.5 volts on a 12 volt, 6 cell battery), the batteries could be expected to recharge only about 3 times! If lightly discharged, they would come back hundreds of times.
Most RVers and off-grid users set personal limits of only discharging deep cycle batteries down to 80% full or at worst 50% full in order to extend cell life. Stopping at 50% full, a 100 AH deep cycle battery provides 5 amps for 10 hours, or 2.5 amps for 20+ hours.
I don't want to discourage you, I myself fully intend to back up a semi-reliable grid connection with generator, battery plant, and inverter. That is 2/3 of a solar system. Just add PV panels and a charge controller. But go into this with your eyes open, and do your research.
Experiment on the cheap, but be prepared to spend for quality permanent components if you want to sleep peacefully at night. My "on the cheap" experimenting has started with a pair of 2kW portable inverter gennys that can be paired, and converted from gasoline to propane. I need to figure out how to get 240 volts for the well pump, either using a big transformer to step up the voltage, or maybe a smaller transformer to 'trick' the inverter gennies to output opposite phases for the necessary Line 1 and Line 2 hot outputs.
There are also new battery chemistries that are interesting. Lithium Iron Polymer (LiFePO) batteries support high current output and multiple recharges, but are still very $pendy. And the light weight of LiFePO cells is not a factor for stationary battery plants.
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