How to adjust usable capacity on older aging battery?

Batteries are electro-chemical devices which are subject to aging, which presents itself as slowly fading usable capacity or reduction in usable runtime. Aging process includes calendar aging as well as charge and discharge cycling. Even if battery is lightly used it still experiences calendar capacity fading due to slow irreversible chemical reactions inside the cells, gradually reducing amount of active lithium ions. This process can go slower or faster depending on average ambient temperatures and average State of Charge (SOC) at which the battery spends most of its life. 

Even though LFP battery should be charged to 100% regularly to maintain cell balance and accurate SOC measurement, it should not be stored at the 100% SOC for prolonged periods of time, like a month or more at a time. Even a small discharge to 95% - 98% would reduce the voltage, which reduces the aging process. When storing for longer periods it's best to discharge to at least 80% - 85%, ideally to 50% - 80%. Please see our storage guide here for more details on how to store your battery.

Capacity fading is a non-linear process, it starts faster in the first 1-3 years, when the battery can lose up to 10% of its usable capacity, then slows down and eventually drops by 20% - 40% over the years. This process is accompanied by deeper voltage drops when running heavier loads, such that low voltage and reserve voltage levels are reached sooner, reducing the runtime of the battery before it needs charging again. 

Reduced runtime leads to innacurate SOC measurements since SOC is calculated as a percentage of a previously set nominal value, equal to the nominal AmpHours capacity of the battery at the date of its manufacture. This value needs to be reduced as the battery ages to account for fading capacity. This can be done automatically on batteries with latest BMS hardware and firmware levels, as described in this guide. However, an older BMS version such as External BMS Version 8, a.k.a. BMS V8, is not capable of usable capacity calibration and needs to be adjusted manually following below steps.

1. Charge your battery to 100% SOC using shore power. It's important to actually observe the 100% on your Lithionics Battery monitor app at the end of charge, not 99%, which can be innacurate due to previous SOC drift.
2. Swipe left on the Lithionics Battery monitor app screen to access the Details screen and take a note of the current Total Consumed counter. Write this value down as a starting position.
3. Discharge your battery within a 24 hours period using any available loads, such as lights, DC fridge, Air Conditioner, etc. Try to avoid heavy loads where deeper voltage sag could further reduce the runtime. Typical discharge time should be between 4 and 24 hours, until battery reaches Reserve Volate or Low Voltage and BMS shuts down battery power.
4. Reset the BMS by pressing the On/Off button, turn off heavy loads and start charging your battery using shore power.
5. Access the Details screen in the app again and take a note of the increased value of Total Consumed counter. Subtract starting value from ending value to obtain current usable AmpHours capacity of your battery.
6. Access Terminal Console screen in the app by touching Gear icon in the upper right corner to open Settings screen, then touch Terminal Console button to open it. At the bottom there is a line with $ prefix where you can type a command $AH=nnn , where nnn is the usable capacity calculated above, then touch Send icon to execute the command. You should see an OK response scrolling up in the console above, indicating that command was accepted.
7. Fully charge your battery to 100% again to re-sync the SOC meter with the new AH value.