Intermittent charging problem in timed charge mode

I used the web portal "timed charge" to set my inverter to charge the battery from the grid during an Octopus "Power-ups" session 11am-1pm today, as I've done successfully many times now. However today the battery only charged intermittently rather than continuously as it has done in the past; and only reached 20% full rather than the expected 60% ish. This is the power graph from the portal.

There are no error notifications or messages or alerts in the portal interface. What could be causing this? Is it likely to be a hardware fault?
This is a GIV-HY5.0 inverter with a 9.5kWh battery and 7.5kW PV array, installed about 3 months ago.
Thanks for any suggestions.

davebiff What temperature was the battery at when you started the charge? Looks like it spent the entire night idle so if its somewhere cold then that would explain things....

Vestas Thanks for the idea, I did wonder about the cold weather being a factor. The "battery data" tab says the battery temperature was 1-2°C from midnight to 11am. The system is installed in a carport so it's somewhat sheltered. The GivEnergy datasheet says the battery operating range is down to -10°C though?

davebiff That explains it then.

The battery (or rather the cells in the battery) will discharge (at greatly reduced rates) down to -10C. Hence the spec.

It won't (or shouldn't) charge at all at or below 0C - it'll cause irreversible damage to the anode of the cells.

Below 5C it should charge at a reduced rate but this isn't a great idea if you want to maximise lifespan.

There's another thread running about temperature and batteries which got posted to a couple of days ago which is probably worth reading.

The tl;dr version is that lithium-ion batteries really don't like being charged below 5C and it should be avoided when possible.

Vestas Thanks for the insights. I'm a bit surprised (and annoyed) that this isn't flagged up for outdoors installations - it's not like cold weather is uncommon here. The installer specifically refused to put the system in the loft (my first choice) because it would get too hot, but didn't mention the possibility of getting too cold in the carport. And the GivEnergy docs include cute little pictures of systems on external walls with snowflakes and a tick, which is misleading along with that datasheet...

Anyway. Grumpy, but not with you. 🙂 To make the best of it I guess I'll look into insulating the battery for the winter months. Another thread suggested attaching insulating board e.g. Celotex directly to the battery. Is that safe or does it need some clearance for ventilation?

davebiff I fully agree with you - a friend in Ballater has a Powerwall on an outside wall and has no problems of this sort. Was -9C where he is last night, currently -5C and the battery works just like it does in summer so its clearly a design flaw on the part of GivEnergy.

I'd suggest (as I said in another thread) that you get some heavy-duty velcro tape, cut some PIR to size and attach it with the tape. Then you can monitor the temperatures and see how it goes, easy enough to add/remove until its right.

Lofts are a dreadful place for lithium-ion batteries (heat is the #1 cause of reduced battery life) or inverters (they'll be derated at temps above 40C).

Thanks for the advice. Now the weather is a bit warmer, I was able to charge the battery to 100% with no issues, so it does look like the cold temperature was the cause. GivEnergy have proactively responded and said they'll book a site visit too.
I have a couple of friends with battery/inverter systems in the loft, they haven't reported problems YET (maybe time will tell).

davebiff They won't be aware of them unless they're aware of what derating is and the effects of heat on lithium-ion batteries - they'll just think its normal 🙂