Simulating a Power Outage to Test Battery Health

Batteries that are used strictly for resiliency are oftentimes rarely discharged, as these storage applications only get used when the utility has an outage. That has a lot of implications for the storage equipment. Join HeatSpring instructor Chris LaForge as he explains how to simulate a power outage with a PV + battery back-up system and why it’s important for customers to regularly check their battery’s health. 

There is maintenance with lithium ion.  It’s not nonexistent, mostly observation. Then as a client, they’re going to watch their system operate and know that it works. And if you’re doing a grid-tied battery backup system, that means flipping off your main breaker once in a while.

Because if your battery’s primarily there for resilience and you don’t test it with an imitation power outage once a year or twice a year, you have no idea how the health of that battery is going. Nothing tells you anything about it. 

Basically, your system’s going to keep the battery fully charged. The first time you’re going to find out whether it’s not happy or not is in a real power outage – that’s stupid behavior. So we train our clients to flip the main breaker off  twice a year. Hopefully, they do it at least once a year and run a day and see how the battery supplies the energy that you want during power outages.

Is there any surprise? Is the battery getting depleted too quickly by your estimate? That means there’s a problem with the health of the battery. I’ll tell you one thing that’s really bad news for people that just have these batteries sitting there for resilience is that batteries don’t like to just sit.

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Batteries are designed to cycle and they know what they are based on that activity – charging up and discharging. Now, lithium ion is kind of nice because it’s not like the early Ni-Cad batteries. If you don’t drain it all the way down to a very, fairly useless stage, and you charge it up when it’s half capacity, it starts to think it’s a smaller battery. 

That’s always been a nuisance in operating Ni-Cad batteries. Well, lithium ion is a little bit nicer than that. It doesn’t have the memory effect that Ni-Cads do, but lithium ion is still a battery. It still wants to know it’s loved and it is useful. That comes about by draining it down and charging it up. 

I’m going to be kind, because I’m a nice person. I’m from the Midwest. I’m not going to say they’re really dumb batteries, which may be what I think. But I will say these resiliency batteries have such a narrow service provision – they’re just there to give us power during power outages. We need to make them work from time to time.

This test of your battery that I’m telling you about is a battery cycle. And that’s what you want to do to your battery. If I was on-grid with the grid -tied battery backup system on a residence or a small commercial system, I would create a power outage to the battery and make the battery work quarterly – at a minimum. Give it four cycles a year. 

Chris [meaning myself] is a battery nerd. He’d do it every month. That’s going to tell the battery that we expect you to be there, and we’re going to discharge you down with lithium ion, supposedly to maybe a 80% depth of discharge. Then we’re going to watch how fast it charges back up.

Remember a dying battery not only loses its voltage quickly under load, it acts like it’s charged up faster than it should too. That means when you put the charge on it, its voltage is going to spike high and stay high. It’s going to look full because –  Hey, that’s the full battery voltage. But actually the battery has all this internal resistance and it’s been dying for a while. It’s probably close to being dead. 

Unless you know the signs –  which is rapid discharge beyond what it should have based on no capacity, and also rapid recharge based on the fact that it looks like it’s getting to a charge voltage, but it’s really just full of internal resistance as every dead battery is.

Those are the main service things we want to get through. How often do you do that? I tell people to do their maintenance every year.