What is state of charge?
State of charge, or SOC, expresses the charge remaining in a battery relative to its maximum possible charge [S1]. An assumed 50% reading means half the charge on that stated reference basis. For your site, check the minimum operating reserve and available capacity before translating a dashboard percentage into usable energy. Checked October 2026.
What does state of charge mean for your site?
State of charge, usually SOC, is a measure of how much charge remains in a battery. SAM’s technical documentation defines it relative to the maximum possible charge [S1]. Think of it as the current charge level on a stated reference basis.
Ask the installer what the displayed percentage represents. Request the corresponding available energy and the reserve setting in the handover documents. A percentage without that context leaves you unable to assess the energy available for your planned use.
How can you estimate energy above a reserve?
Illustration, not a quote: assume a simplified battery energy model with 100 kilowatt-hours (kWh) of current available capacity, a 70% charge reading and a 20% minimum reserve. Treat the percentages as energy fractions for this example. The usable window above the reserve is 70% − 20% = 50 percentage points.
The calculation is 100 kWh × 0.50 = 50 kWh before conversion and auxiliary losses. These assumed settings do not establish an equipment operating recommendation or backup duration. Ask the installer to confirm actual delivered energy and the loads the system can support.
Read backup power with battery sizing before setting a reserve requirement.
How do operating limits affect battery use?
SAM allows minimum and maximum SOC settings and explains that the available capacity reference changes with degradation [S2]. A procurement model should therefore identify the capacity basis and configured limits.
Ask for the proposed daily operating schedule, who can change the reserve and how you will see those changes. If maintaining a backup reserve is part of your brief, request a demonstration of that control during handover. Keep those instructions with your site operating procedures.
Use depth of discharge to understand the size of a discharge window and round-trip efficiency to understand energy losses.
Next step
Get matched with an installer that covers your area. Piggy Pineapple Ltd operates this referral service. We refer enquiries to installer partners and may be paid a fee. Our owner holds shares in at least one partner. Before sharing your details, we name the proposed partner and disclose any shareholding in it.
Common questions
Is state of charge the same as battery health?
No. SOC concerns the charge currently present. SAM separately reports capacity changes caused by degradation. Request both the operating charge limits and the capacity basis when comparing proposals [S1].
Does 100% state of charge always mean the original rated capacity is available?
No. SAM's operating-limit guidance explains that percentages refer to available capacity, which can decline as a battery degrades. Confirm how the proposed product defines its displayed percentage [S2].
Does a minimum state of charge setting limit discharge?
Yes. In SAM's example, a 15% minimum stops discharge below 15% of available capacity. That is a modelling example, not a recommended setting for your equipment; obtain the installer's proposed limits [S2].
Ask about your site
Sources
- Battery Results, National Laboratory of the Rockies - System Advisor Model,Last checked 16 October 2026
- Battery Dispatch FOM, National Laboratory of the Rockies - System Advisor Model,Last checked 16 October 2026