A homeowner planning to expand a solar backup system posed a question many battery owners eventually run into: When adding another battery, does the new one need to exactly match the one already installed?

Here's what to know

On Reddit, the poster wrote, "I want to add a second battery," and explained that they already had a RUiXU 12k inverter and a RUiXU Lithi2-16 battery, both installed in December 2025.

They asked about two things: whether the second unit had to come from the same manufacturer and whether a difference in age could create problems.

One commenter replied, "Within a year you can probably do it without issue if you add the same battery as the first (not 'about the same')."

Home battery systems often rely on battery management systems, or BMS, to communicate with one another and with the inverter. Homeowners considering an expansion can also explore EnergySage to compare home battery storage options and get competitive installation estimates. EnergySage has teamed up with the electrification brand Qmerit to guarantee you get the best price on home battery storage solutions.

Pila is another company offering excellent battery backup options.

More background

Commenters suggested that matching size alone was not enough, because the batteries also need to communicate properly.

One warned, "It is quite likely that they use different bms solutions and while similar that could cause problems."

Another said the batteries should support "master / slave config and communication between the batteries" if the inverter depends on that data.

Adding battery storage can protect a home during outages, save money on energy, and increase energy independence. It allows households to store excess solar production or cheaper off-peak electricity for later use, helping reduce utility bills during expensive evening hours and avoid the fuel costs tied to backup generators.

If a second pack does not communicate properly with the first battery or the inverter, homeowners could end up paying for equipment that underperforms or needs to be replaced.

What can be done?

The poster asked, "How are you supposed to know that?" — leading another commenter to point to the most basic place to check: "Spec sheet?"

Those documents can help confirm voltage, communications protocol, and whether the system is meant to run in parallel with another pack. That question came up directly in the thread, with one commenter asking whether the added battery would go in series or in parallel.

Another commenter noted, "Almost never in series assuming the current one is a match for the inverter's supported battery voltage. It's very unusual for an inverter to support both 48v and 96v."

One commenter summed up the concern about switching brands instead of buying an exact match: "It migjt work but I wouldn't risk my money if it were my system."

Where can I learn more?

These articles cover home backup batteries, battery quality concerns, and other homeowner energy upgrades.

• SunPower and Palmetto offer backup batteries without upfront costs for homeowners.

• A DIY solar expert found badly crooked cells inside a bargain Amazon battery.

• One homeowner said his solar setup works after skipping battery storage for an EV charger.

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