Victron Super Cycle AGM Batteries Failure

[DragonflyBob]

Last October, we replaced two of our house batteries (West Marine 55aH AGM) with three Victron 60aH Super Cycle AGM batteries. These were drop in replacements as our boat (a 2016 Dragonfly 32 Supreme) was already set up by the builder for up to three house batteries. We had not had any issues with the West Marine batteries but we wanted to increase our house capacity and the other bonus was that the Victron Super Cycle batteries were lighter and could be discharged deeper than a standard AGM. At the time, we did not change out our starter battery (another West Marine 55aH AGM) and I had replaced the 70aH bow thruster/windlass battery about 6 months prior. The boat’s electrical system is set up with an isolator relay to separate the engine and house banks for charging and the bow thruster/windlass battery is set up in parallel with the house bank.

The new batteries performed flawlessly on a two week cruise right after we got them as well as all the sailing we did during the winter and spring. We took a 3 week cruise with the boat in late April and again the batteries performed flawlessly. In use, we have never seen the voltage on the batteries drop lower than 12.1 volts. When the boat is at its slip, charging is handled primarily by a Quick NRG 250 AC charger that can provide up to 25 amps of charging current. Typically when we check the boat in the slip plugged in, the batteries are at 100% charge. We always leave our refrigerator and a 12V freezer running so the house battery voltage varies from 13.6V (float) to 14.1V (charge). We have an air conditioner installed on the main companionway hatch that also runs on shore power and keeps the interior of the boat around 75F day and night.

About a month ago, we came down to the boat and when we entered the cabin, there was a slight weird odor. My wife went to turn on a cabin fan and she stepped up on the hatch over the battery compartment and felt warmth on her feet. I immediately opened the hatch and found that the Super Cycle batteries were all warm to hot and had bulged out outer casings. One battery I estimated to have around 140F outer temperature (almost too hot to touch), the second was probably around 120F, and the third around 110F. The degree of bulging was worst on the hottest battery and just very slight on the coolest battery. I checked the engine and bowthruster/windlass batteries and they were both cool to touch.

We shut down the 12 volt system in the boat and removed the Super Cycle batteries. I reinstalled the two West Marine batteries the Super Cycle batteries had replaced and to date all is normal. We have checked the boat at least 8 times since and the batteries are always 100% charged and always cool to touch.

We purchased the Victron Super Cycle batteries from Ocean Planet Energy (OPE). We reviewed the application and electrical power setup of the boat prior to purchase and they gave us the green light for the upgrade. They don’t see any “red flags” on the boat’s electrical system and are pursuing a warranty claim on our behalf with Victron as they cannot see anything in the boat’s electrical system design that would cause this to happen.

We also reviewed what happened with Quorning Boats (the builder of Dragonfly trimarans). Their electrical engineer indicated to me that they were not aware of any similar incidents and the design and setup of the boat’s electrical system today is basically the same as it was in 2016 so they have high confidence there was no fault in the system to cause the thermal issue.

The batteries are now at my house while we wait for a response from Victron. If I check voltage, all three are still at 13.3V to 13.5V. I can only guess at this point that perhaps the battery that was the hottest might have an internal fault that led it to be overcharged and this affected the other two batteries. I’m hoping Victron can take the batteries back and do forensics to see if this is the case.

Wanted to post this here to see if anyone has seen or experienced a similar occurrence.

[wholybee]

That sure sounds like overcharging, just about nothing else it could be. I couldn't tell you what went wrong to cause it, but that is what happened. Maybe the charger behaves differently with 3 batteries connected vs. 2? Maybe the Victron require lower voltages than the West Marine? Maybe the charger went into some sort of equalization charge? Maybe some event was causing the charger to stay in bulk/absorption and not change to float?

You mentioned that when plugged into shore power it normally changes between float an absorption. That is not normal. Once charged, it should stay in float. Even with Refrigeration etc. cycling on/off, unless those loads are pretty large, the charger shouldn't kick into absorption because of them.

Unfortunately, it's impossible to know now, unless it happens again. You would need to do some tests, voltage, current, and check any lights on the charger, while the event is happening.

[DragonflyBob]

Originally Posted by wholybee

That sure sounds like overcharging, just about nothing else it could be. I couldn't tell you what went wrong to cause it, but that is what happened. Maybe the charger behaves differently with 3 batteries connected vs. 2? Maybe the Victron require lower voltages than the West Marine? Maybe the charger went into some sort of equalization charge? Maybe some event was causing the charger to stay in bulk/absorption and not change to float?

You mentioned that when plugged into shore power it normally changes between float an absorption. That is not normal. Once charged, it should stay in float. Even with Refrigeration etc. cycling on/off, unless those loads are pretty large, the charger shouldn't kick into absorption because of them.

Unfortunately, it's impossible to know now, unless it happens again. You would need to do some tests, voltage, current, and check any lights on the charger, while the event is happening.

I agree that the most likely cause of the overheating was overcharging of the batteries. I might have mis-stated on the battery voltages we observed on the displays in the boat. I’ve certainly seen 14.1-14.3 volts in charge/bulk/absorption mode when the batteries have gone down to 12.1 - 12.3 volts when we are out cruising and we start the engine or plug in shore power if we arrive at a marina. When the boat is at the slip in our home marina, I now believe I have only seen the batteries indicate 14.1-14.3 volts after shore power has been disconnected for whatever reason (we returned from a day sail, moved boat to another location in the marina, etc.) and we than re-connect after a period of time to where the engine or the solar panels did not contribute to keep the batteries at 100% charge.

What I will do now is spend some time at the boat in the next week at its slip with the AC charger on and monitor the battery voltage to see if it remains in float mode with the batteries we reinstalled. The only 12v consumers would be the boat fridge and freezer which combined typically draw 3-5 amps so between the solar panels output and the AC charger output, that should always keep the batteries in float mode.

The fact that the engine and bowthruster/windlass batteries did not heat up when the Super Cycles did and currently there seems to be no issues with the previous house batteries re-installed sure seems to point to some fault specific with the Super Cycle batteries. That’s why I believe I have to get the batteries back to Victron for an “autopsy”.

FWIW, I’m kicking myself that I did not confirm the battery voltage on our displays when we discovered the overheating issue. I was just totally focused on taking those batteries offline.

One more question. If we had not discovered this, what would have likely happened? Could the batteries have continued to heat up and explode (or catch fire)? We are obviously a bit rattled by this incident.

Thanks!