How do you actually know if your battery is healthy?

DIY
, , , , ,
1

If you have a Victron system with VRM.
How do you actually know if your battery is healthy?

1 Like
2

What does healthy mean to you?

There is a state of health for some LFP batteries provided by their BMS. I assume it represents the amount of dis/charge cycles left, or the amount of usable capacity left compared to the original value. I dont think its a particularly helpful value.

If you want to know the state of charge however, you either need a battery which can communicate with the GX or need to use a shunt.

3

VRM can’t tell you if it is healthy, it can present a series of metrics that can help you interpret battery performance.
Your question is unfortunately way too brief, you will need to flesh it out a bit if anyone is going to understand what you are trying to achieve.

4

I was thinking that maybe analysing data from VRM could indicate the battery status and how healthy is is right now. For example compaired since it was connected.
What do you think?
Is there anything else needed to do this?

5

What type of battery is it? Managed? Shunt? etc? This affects the data that is available, the states it can send.
Lithium batteries you would compare min/max cell voltages.
You would look at how it holds its charge under load and over time.

State of health is a mostly useless statistic for lithium.

6

What is needed? and how do I know? Im open to suggestions since Im no expert.
My guesses is that needs component that produces VRM data and battery monitor is good to have?
Would like to know for any type of battery not limited by type. But lets say a litium battery.
I know it is wide question and it is intended so.

7

I have my own way of measuring battery health.

If the battery covers my needs then it’s healthy

If the battery goes flat during normal use then it’s not

Or it’s not a big enough battery

5 Likes
8

Short answer: you don’t know. Longer answer: you get to learn about the correlations between reported SoC, resting voltages, voltage drops under load, observed (re)balancing needs, observed changes of the SoC - resting voltage correlations to detect capacity changes and then still get to do full capacity test cycles one in a while. A healthy battery is a battery where that ‘while’ becomes manageable with acceptable outcomes in relation to the price/quality quotient of said battery.

1 Like
9
  • Charge it to 100%
  • Discharge it to 0% (don’t worry, you’ll not damage it)
  • Measure the discharged energy.
  • Charge it back to 100%.
  • Measure the energy needed for charging back to 100%.
  • Observe, during entire process the minimum and maximum cell voltages if you are able to.

If you have an efficiency above 95%, it’s OK.
If the difference between the max and min cell voltages is below 30mV, you are also OK.
Do these, come back with values and we can say more.

1 Like
11

Thank you for input. Im ln learning phase.
What is resting voltage?

12

Thank you. Interesting.
Regarding cell balance. Where can I get that information? BMS? No VRM I guess.

13

If it was so easy…..unfortunately not:

State of health is a complex view of aging mechanisms and stress factors.Aging is commonly grouped into loss of active materialsand resistance increase.Stress levels are temperature and charging/discharging levels and times.So it is a multitude of factors.There’s calendar aging and cycling aging.With the charge and discharge stress there’s also charge-discharge-rate,average-state-of-charge,depth-of-cycle and charge/discharge cut-off voltage.

If you have got a JK BMS you might try a nice little monitoring app which is to find at cepower.org

This is not an advert,I have actually helped testing this app and regarding to other monitoring apps it calculates the SOH fairly precise,taking the above criterias in consideration….You could do a hell of a lot of testing,but a simple charge/discharge will only give you a certain idea of capacity degradation under certain conditions.Best regards Frank

1 Like
14

Usually the BMS is supplying that information. And if the Venus OS receives it, it will be on VRM.

1 Like
15

For the battery capacity test, watch some of the videos from “Off Grid Garage” on YouTube.

1 Like
16

Thank you sounds good :slight_smile:

17

Thats a good channel. Thank you. I will check it out.

18

‘Usually the BMS is’ seems a stretch here :wink: Based on the fact that this SoH bookkeeping issue was already solved in the ‘BMS’ of my 14 year old 22kWh Renault Kangoo EV, I would say 'Modern battery suppliers could and should build good quality and SoC and SoH measurements into their BMS systems but most of them refuse to do so to save a few pennies and the market nor any ‘authorities’ are holding them accountable for that (yet). This ‘problem’ does not exist in the much more regulated automotive industry, and technically it has been solved ‘ages’ ago.

1 Like
19

Thanks for the insights everyone.
It is not an easy subject thats clear.
It seems there isn’t a single clear indicator of battery health in VRM. Most people look at a combination of things like cell balance, voltage behaviour under load, capacity tests and long-term trends in the data.

Interesting to see how different people approach this.

20

Victron explicitly delegates the responsibility for providing that information to the (technically correct) system component: the battery. So unless you buy a Victron battery, you will have to take that up with your battery supplier. That does leave something to be wished for as the VenusOS / VRM platform would be well positioned to ‘fill the gap’ between what the battery suppliers ‘deliver’ and what is technically feasible to ‘reconstruct’ based on the raw data that most batteries do deliver. But I know of no efforts to do so at the moment.

1 Like
21

Here is what I used to test one of my 7 yo LFP batteries. Using one of these Battery Tester from Amazon. It worked well over night as I set it to draw 10Amps (130w) about 2/3rd of the testers capacity. Took 17 hours to draw 172Ah of juice from my 170Ah Renogy Battery. I am charging that one now and started testing the second one after figuring out how to clear the data from the first test. I must admit, I was a bit shocked it had Over 100% of its capacity still available after 7 years of use (6 months of travel each year)
The Test Rig Hooked Up

The first Battery Capacity Results

-Bill

2 Likes