question

It looks like your battery has lost a serious amount of capacity to drop that much voltage with a load that small.

@Sampeett I agree that your battery resting voltage appears high; normal resting voltage of an AGM battery is typically around ~12.8v. I suggest reaching out to your battery manufacturer regarding this, or taking the battery and having it tested.

Dropping under load, however, is exactly how it works... when you apply a load to a battery, the voltage will drop. This behavior is significantly less when using an LFP battery, but still present - it's simply how a battery behaves.

In your case, you have a very small battery (95Ah = ~47Ah usable) so the voltage will drop rapidly even under relatively low load, so this behavior is as expected. I certainly recommend that you upgrade your battery bank; this may end up being required if, after a battery test, you discover that you need a new battery.

So, in summary: Battery voltage dropping under load is normal and expected. Your high battery resting voltage is probably not normal, so please check with your battery manufacturer regarding the expected resting voltage of your battery, and then -unless they say that ~13.7v is normal- go have that battery checked.

Thank you for all this information. It is very strange as the battery is brand new, any ideas as to why is drops so fast under load? If I had left the load on surly it would have gone past 12v which could damage the battery? I worked out it should last days if not weeks running just lights and a fan before dropping to

Well I presume it was at rest, there was not sun out for the solar to take. I don’t really understand how the MPPT works. On the app the load was set to always off so I turned it on to always on was this a mistake? I did read an article saying 13.8 was the float state of charge?

sorry for all these questions, I am very new to this.

kind regards

Hi @Sampeett

If your battery is 'brand new', it likely just needs some work to fire it up. Many batt makers actually publish info saying that full rated batt capacity isn't developed until subjected to quite a few cycles.

Akin to an athlete running a race, but limbering-up beforehand. Yours is just rolling out of bed.. :)

And your tiny Wh history isn't helping do that. That's nothing, and your athlete needs at least a couple of stretches before breakfast. Don't get excited about V at this point, just try to remain aware of how much you're taking from the batt. The rating of that batt suggests > 1000 Wh capacity, and to draw it down 300 Wh/d would be a very safe level once it's fully broken in. Fooling about at < 20Wh/d won't get you there.

And oh, I note you have User-defined your V charge settings to higher levels. I'd revert to one of the lower stock algorithms, regardless of what you read of lab figures from the batt maker. Long life, eh..

Hey, 13.8V at idle of a completely new battery is fine. I recently bought a new battery (200Ah) Wich I have cycled a couple of times now and when I have no load and fully charged it sits around 13.1V.

I have a 15Ah, too. I cycled it around 8 times with 7A because it sitting in the shelf a lot and now it stays idle 13.5V. That's normal at AGM. You can safely discharge it down under 12V. But don't go beyond 10.5V. Since 10.5V is the lowest the cells could handle before taking damage (Discharged my little one to 9V accidentally but charged it directly).

The best is, wait for a sunny day and then pull some amps to discharge and let it charge up again. Do this 3 to 4 times and your battery will get better.