No power to 75/15 and smartshunt

DIY
,
1

Hello,

I have a brand new life po4 battery connected to my 75/15 charge controller and smart shunt. The battery instructions say store at 50% soc which i did. Today i thought i would check the system and the app did not pick up the shunt or controller.
I checked and no lights on either. Connected the battery to a victron charger an it came on. Seems like the battery voltage dropped to 11.06 in about 3 weeks from about 12.5 v when it showed 51%soc.
Any ideas as to why this would happen?
Nothing is connected to the battery that could draw power

Screenshot_2025-07-21-18-50-34-27_30b6efbd53acd6f273baafa7ca03da38
Screenshot_2025-07-21-18-50-34-27_30b6efbd53acd6f273baafa7ca03da38720×1612 97.5 KB

Thanks
Archie

2

@Arch
Hi Archie,

Some lithium batteries have a sleep function.
So it is likely that.

It can -on some -also be activated for smaller ‘parasitic’ loads, such as self discharge and very small loads.

For real storage conditions, the shunt and mppt should not have been connected either.

3

Ok thanks lx, will get it back to 50% and disconnect everything and see what happens.
Thank you

4

I see the soc remained at 51% as i left it before shutdown. I think the voltage was 12.5 with the 51%
Now it has the same soc with the low voltage?

5

Yhe SmartShunt does not use voltage to srt SOC. It starts at 100% with a full battery. It then counts the energy out and the energy back in. When it is disconnected, then reconnected it can remember the last SOC value. If in the meantime your disconnected battery has self discharged then the shunt knows nothing about this. When you restart the system you need to recharge your battery fully with the shunt connected so they become synchronised as full battery and 100%.

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