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AiLi Battery Monitor "% remaining" accuracy???

Directshort

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Jul 14, 2020
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I know this is a popular meter and I really like it so far for voltage readings and amperage draw and it's tested to be accurate for that but just wondering if the "percentage remaining" part of the shunt is usually accurate?

I calibrated it initially by fully charging the battery and it appeared to work fine for a while but after a couple months the "% remaining" function seemed to be wrong as far as I could tell by comparing to the voltage reading. But reading state of charge using voltage I think is the tricky part with Lifepo4 batteries since the voltage range is small.

I used the Xuba 280 homemade pack with Overkill Solar bms and that performed amazingly well so far and I don't want to ruin it by over-discharging it too much so would like to figure out the % charge thing. I am a total newb at this so don't want to talk negatively about the product it's surely something I am doing wrong.
 
It does not base % remaining on voltage. It counts the current passing in and out of the battery and computes a % based on the programmed battery capacity an net current flow.

Unfortunately, their accuracy drifts over time. It's important to periodically fully charge the battery to 100% and calibrate the meter at that point.
 
I never did the recalibrate and it's been months so will give that a try.
Thanks for the help really appreciate it.
 
Victron indicates that their BMV units need to be self-calibrated to a 100% charge "a couple times a month."

If you're intentionally running the cells at a lower state of charge as their peak, you might consider redefining 100% as YOUR 100%, e.g., if you're charging to 3.5V/cell and terminating at 0.1C, you should program your 100% to that "full charge" criteria.
 
Thanks you just answered my other question that is if the drifting was specific to the cheap meters or applies to all types of those shunt sensors.
 
Nothing has 100% coulombic efficiency. Losses due to voltage drop, cell internal resistance, charging inefficiencies, etc., will always skew the values over time.
 
When is best time to tell monitor battery(s) 100%?

IE: after bulk charge into absortion? After absortion going to float? Reason I ask is I am full time in rv and don't want to take off cables and let batteries sit idle for an hour......
 
Not sure why you would let your batteries sit idle for an hour. These devices are not voltage based.

By definition a battery is fully charged when the charge termination criteria are reached. This is typically at the absorption voltage and the "tail current" - when the current drops to some % of battery capacity (5% for FLP, 2-4% for FLA/AGM/GEL).

You want to set it to 100% when the battery is fully charged. A properly programmed battery monitor recalibrates to 100% when the charge termination criteria are met. It can be hard to get this to happen perfectly, but if you're near the transition to float, you're close enough.

The little jump in mine is only 1-2%. I'm tweaking this with each day's charging, but it's hard to get it just right. Next adjustment is likely to eliminate the jump, but delay 100% for 30 minutes past float. One has to be okay with "close enough" :)

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