Update: Epoch’s 460ah battery, what we’ve learned

In January of this year, I published my review of the Epoch 460 amp-hour, 12 volt battery. My review was quite positive and reflected how the battery performed in my testing. But, once the battery was in the wild, reports began trickling in of troubles with some installations of the 460s. That lead to weeks of investigating the issues. At this point, I believe I have a solid command of what’s happening with these batteries and some of their limitations. While this better understanding of the batteries does serve to take a little shine off them, I still believe these are very solid batteries and capable of delivering excellent service. But, for best service, some tuning is required.

A word of warning, we’re going to get quite technical on some of the issues I’ve encountered. If my explanations fall short or I confuse anyone, please drop a comment at the bottom and let me know. I hope this entry will help people understand the issues and how to work around them,

Full charge protection

Charging LiFePO4 batteries at high voltages for extended periods of time isn’t good for them. Continuously charging LiFePO4 cells at a high voltage can cause dendrite formation. Dendrites result in reduced capacity and potential internal failures in cells. My research indicates there isn’t a clear understanding of the exact causes and prevention of dendrites, but there is a widely held understanding that overcharging LiFePO4 cells is directly linked with dendrite formation.

Most companies selling lithium iron phosphate batteries offer long warranties. In fact, the norm is for some form of warranty stretching out to ten years and beyond. As an aside, I encourage you to look at the actual terms of these warranties not just the big bold print. Many offer three to five year full replacements followed by a meager discount for the remaining years. In order to offer long warranties, battery manufacturers want to ensure the batteries will protect themselves.

The battery management systems or BMS in LiFePO4 batteries offer numerous protections for the battery. We’re familiar with quite a few of those including high and low voltage cut offs at both the pack and cell levels as well as temperature protections. But, more recently we’ve started to see, or perhaps more accurately notice, protections against high voltage charging for extended periods of time.

To protect against damaging voltage for extended periods of time, the BMS in the battery disables charging if charge voltage is observed to be above 14 volts while current acceptance is below 3.5 amps for ten seconds. It turns out this protection has been present in at least some of Epoch’s batteries for quite some time. I’ve observed the same behavior in the 100 amp hour batteries I reviewed early last year. This behavior also has a couple of potential unintended consequences, let’s take a look at each of them. Also, note that Epcoh isn’t alone in using this protection mechanism. In fact, it’s becoming increasingly common.

High voltage alarms

The video above demonstrates what happens when the full charge protection kicks in. If charging comes from a stabilized power source, like a lab grade DC power supply, there won’t be a spike because the power supply stabilizes its output without a battery connected. But, most people don’t charge from a bench power supply. Instead, they charge from alternators, inverter/chargers, and dedicated battery chargers. Inverter/Chargers and alternators generally depend on a connected battery to assist in stabilizing output voltage. Some battery chargers need a battery connected and some don’t.

In the case of charging from inverter/chargers and alternators, when the battery suddenly stops charging, the energy coming from the transformer or alternator needs to go somewhere. Applying Ohm’s law, we find that increasing the resistance — by opening the charge MOSFETs — results in increased voltage. The spike has a short life and decreases once the charge source reduces its output.

Unfortunately, during that spike, the battery sees high voltage and raises an alarm. In reality, this alarm is basically a nuisance, but it’s a nuisance that requires clearing the alarm on the Victron GX device to stop it from beeping.

Uneven discharging

I only have one 460 on my test bench so I haven’t been able to reproduce the issue, but I have received several reports of uneven discharging. I’ve heard reports from both boat owners and technicians who have deployed multiple 460s in parallel banks. They’ve reported circumstances where either only some batteries have entered full charge protection or one battery stays in this state longer. They then observe that the battery in full charge protection seems to carry less of the discharge load than the other batteries.

Avoiding issues

The easiest way to avoid these issues seems to be preventing the battery from entering full charge protection. To do this, we need to set our charge sources below 14 volts so the battery never enters full charge protection. This means setting the absorption voltage of your charge sources below 14 volts. Typically, that is either 13.8 or 13.9 volts depending on the stability of your charge source. I’ve used 13.9 with a MultiPlus 2000va inverter/charger without any troubles. The one caveat to this is that charging at lower absorption voltage means charging takes longer. I’m working on a comparison of both capacity and charge times based on charging voltage. I’ll post an article on that shortly.

The screenshot above shows Victron’s VE Configure connected to the MultiPlus via an MK3USB interface. But, if you don’t have an MK3USB or prefer to configure everything via a GX device, you can leverage DVCC.

Unfortunately, there’s an issue with the DVCC parameters the battery sends. As you can see above, the battery calls for a charge limit of 14.6 volts. That was Epoch’s charge recommendation at the launch of the battery and frankly I think it’s a bad one. Curiously, Epoch hasn’t updated their documentation yet so the online manual still recommends 14.6t volts. However, their sales and support reps do provide the updated recommendation when you contact them.

14.6 votls is well above the 14 volt threshold at which low current charging is disabled. Additionally, 14.6 volts in a four cell battery like this one equates to 3.65 volts per cell. 3.65 volts also happens to be the cell overvoltage protection threshold at which the BMS will disable charging. If any the cells are out of balance at all, and with 460 amp hours of capacity, it is likely there will be some imbalance at the top of the charge curve, one of the cells will tip over 3.65v and generate a cell overvoltage protection alarm and shutdown.

The solution is to modify the global DVCC parameters for the GX instance to limit charge voltage to 13.8 or 13.9 volts. Either method accomplishes the same goal of limiting absorption voltage to below 14 volts.

SOC inaccuracies

In further testing the performance of the 460, I’ve cycled it a lot. I’ve subjected the battery to high and low current loads. I’ve left it sitting on the bench for weeks at a time and I’ve rapidly cycled the battery. Over that time, I’ve come to realize the battery’s own estimate of its state of charge (SOC) is frequently inaccurate. This isn’t new for LiFeP04 batteries with internal BMSes. In fact, I’d describe most battery management systems’ SOC measurements as suspect, at best. As I mentioned in my original review, I mentioned that the battery’s internal current sensing resistor or shunt doesn’t measure current flow below 1.4 amps. In my time with the battery, I see that current flow providing significant SOC drift.

Inaccurate SOC becomes a bigger deal when you transmit it via Victron comms and display it throughout the GX ecosystem. Fortunately, there’s a cheap and easy solution. A Victron SmartShunt is more accurate than the internal current measurement, measures an entire battery bank, and costs less than $120 at retail pricing. If you prefer the remote display of a Victron BMV-712, that’s also a good option at roughly $160 retail.

A good option without comms

I’ve just detailed a number of issues and limitations with the battery. So, you might be thinking this isn’t a good battery or you should buy something else. I don’t think that’s the case. To be fully transparent, I don’t have experience with a non-Victron battery that handles communications better. Nearly every Victron communicating battery I’ve researched has voluminous threads on forums and social media detailing trials and tribulations. To my eye, we are in a state of flux on communications between batteries and power conditioning equipment. Victron deserves kudos for being willing to work with non-Victron branded batteries. But, I also think it’s worth understanding that these integrations are pretty immature at this point. T

So, what’s the solution you ask? In my opinion — and I’ve tested it on several industry experts — the solution is really simple. Unplug the comms and use the batteries as we have been using internal BMS LiFePO4 batteries for several years. You still have the benefit of Epoch’s app via Bluetooth, you still have an excellent battery with a built-in high AIC fuse, and you still have excellent value. $1,999 for a 460 amp hour battery remains among the best prices out there and the density is difficult to beat.

Summarizing recommended settings

Just to reiterate my recommendations based on extensive experimentation, here is what I would do using an Epoch 460 amp-hour 12-volt battery. I would start by getting rid of Victron communications. Then, with the comms cable disconnected, I would go into my charge sources and set them for an absorption voltage of 13.8 or 13.9 volts and a float voltage of 13.4 or 13.5 volts. Make sure you address all your charge sources including alternators, battery chargers, inverter/chargers, and solar charge controllers. Lastly, I would add a SmartShunt or Victron BMV-712 to the bank of 460s. I believe with these basic settings, you will get good service from your batteries and enjoy reliable performance for years to come.