Rotating B300's during power outage

I have an AC300 unit with 3 batteries and plan on getting a 4th later this year. I’m currently using this system as a UPS (devices are plugged directly into it and it stays charged via wall AC when power is on; no transfer switch).

Could I buy a couple extra batteries and keep them charged separately as spares and then during an outage swap out batteries that are getting low for spares or would it be more efficient to use the spares to charge the AC300 while it is in use?

Yes of course you could. I would just swap out batteries myself if the others were dead. But its kind of redundant, Wouldn’t just hooking up the extra batters to the system accomplish the same thing? when the 3 are dead swapping to a 4th isn’t any different than just hooking up all 4 (or more) at once. In the end either the grid comes back on and you’re good or it doesn’t and all your batteries are dead. Another suggestion would be to buy a proper generator or solar panels to keep the unit charged if the grid goes down. For the price of 1 or 2 batteries you could probably buy what you need to keep the system charged up regardless of the grid.

The 4th one that I plan on buying soon will not be used as an extra for swapping out. It will be added to the other 3 to “complete” the system. The extras (for swapping out) would be any that I buy beyond that. Also, aren’t they hot swappable or would I actually have to wait until the system shutdown on its own?

Good question on the hot swapping, I’m not sure if you can or not.

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Yes, you can hot swap the B300 batteries even when under power. Obviously the AC300 will complain by sounding its alert tone and posting several error messages, but it will not shut down or stop delivering AC or DC power.

Now that this theme is posted, I suspect that the original B300 battery production may be halted in the future, since the new B300S substitues it with more amperage delivery ( the cable is rated at 150 A) which works with the AC500 but is not compatible with the AC300. So I ordered two more B300 batteries for my twin AC300 setup and complete the system with four batteries per AC300. I recommend present AC300 owners to buy as many B300 batteries as they can now unless you plan to upgrade to the AC500 which can use the B300.

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@glc650 Because the AC300 system is an off-grid machine, a transfer switch must be required to connect to the home grid. .
You can use B300 as a backup battery pack, but AC300 can only be combined with a maximum of 4 battery packs