Battery capacity - stated vs true

Hi all, I'm a new user (about a month) and have confused myself about battery capacity. I hope someone here can help.

I have two batteries - each is a 9.5kWh GivEnergy battery and I thought I'd read that the usable capacity is actually 80% of the stated capacity but can't find the source of what I read. 80% of 19kWh would be 15kWh (give or take) but I've charged and monitored for 6 hours. Battery status was 26% at the start and 81% after 6 hours. During those 6 hours the inverter reported charging at a consistent 1.19kWh per 30-minute slot (OK, so 2.38kW, which seems believable, although 2.6kW would be nice!).

So 55% was added using/adding (???) 10.71kWh which would suggest 100% would be 19.47kWh. I accept that each battery is unique so 19kWh of battery is likely to be something slightly lower or higher but 19.47kWh suggests that the stated 19.05kWh capacity is useable rather than the 15kWh I calculated after reading the GivEnergy documentation.

Can anyone shed any light?

Thanks
Chris

For completeness I thought the 80% had come from the following theory but can't find where I saw it now I look again...the 4% below which the battery doesn't discharge and the "top 15%" that isn't included when displaying 100% charge (in order to lengthen battery life) meant that only 100% - 15% - 5% (because actually the 4% is 4% of the CHARGEable 85% and not 4% of the total 100%, and 4% of 85% is 5% of 100% [approx]).

The 9.5kWh batteries are deemed 100% DOD - basically they are close on 12kWh batteries but only charged to 80%.

anglefire Thanks for the quick reply. What's DOD?

Depth Of Discharge. 😄

crispy DOD

Depth of Discharge. Yours are about 12kWh but you've bought 9.5kWh of capacity guaranteed for 10 years. The older batteries are more like 10kWh but guaranteed at 8.2kWh for the lifetime.

See this link.

Tim THAT's the article I couldn't find again! Thanks for the reply.

mrand31 Aha!!! Thank you!

Bit late but this is my best effort of all the different batteries, DOD's and usable capacity since they began in 2019

Tim How do I determine the ACTUAL capacity at any point - I'd like to monitor.

Support advised that regular timed charges/discharges can accelerate battery degradation. Any experience of this?

philipdawsonladds Support advised that regular timed charges/discharges can accelerate battery degradation. Any experience of this?

AFAIK all usage degrades the battery, but there is also calendar degradation, ie it will degrade over time even if you don't use it. Extreme temperatures don't do them much good either.

I have a friend with a powerwall that refuses to charge from the grid, to avoid possible degradation. So it tends to sit at a high level of charge all summer, and close to empty all winter. That's NMC chemistry, and in EV circles at least, we're told that's something best avoided. GE batteries are LFP, which I think tolerate high charge states rather better.

I do cycle my battery daily - currently between 10 and 80% - but I try to limit the power: I avoid charging or exporting at full power. There is high demand when preparing evening meal, but battery is around 50% then, so I think it's generally happy there. I've read that cell balancing tends to happen a low SoC.

https://goalzero.com/blogs/news/optimize-lfp-battery-lifespan#:~:text=All%20batteries%20degrade%20over%20time,products%20the%20longest%20possible%20lifespan.

philipdawsonladds if you have the ability to stand up GivTCP with or without home assistant you can read the battery capacity and battery design capacity of the battery, plus battery cycles too

(possibly not for AIO yet, but for all other GE batteries yes).

TX200
There’s a lot more info for the AIO available on the GivTCP beta. Including a score of battery health, and individual cell voltages.

TX200 What is GivTCP? and yes, I can stand up.

philipdawsonladds OK found it - looks challenging!

philipdawsonladds try speak to the geek channel on YouTube, there's some videos on setting it all up.