Victron NG Smart LiFePO4 batteries, ultimate power flexibility

If you made a list of all the features you require and prefer in your boat’s batteries, I would bet that Victron’s NG Smart batteries would check just about every item on your list. In a field where it sometimes feels like we are all field testing products, Victron’s batteries, BMSs, and software evidence maturity and integration most other manufacturers can only dream of achieving. About the harshest thing I can say about Smart NG batteries is that they’re more expensive than some of the other batteries out there. But, stick with me and we’ll take a careful look at what you get for that extra expense.

Let’s start with an acknowledgement of something that might seem obvious. Victron has an advantage when it comes to making batteries integrated with the Victron ecosystem. Since they created the ecosystem, and can modify it to best work with their own products, they have a significant leg up in integrating with it. Many of the batteries I test claim Victron communications abilities. Over time, my testing has shown that the reality is that some batteries communicate better than others. Not surprisingly, Victron’s batteries offer a level of communication and integration with their Venus OS and GX devices that no other battery can touch.

Next generation hardware

The NG in Smart NG stands for next generation. As the name implies, NG batteries and BMSs succeed Victron’s Smart LiFePO4 batteries. NG brings several major improvements including more compact batteries, additional data and alarming from the batteries, automatic battery firmware updates performed by the BMS, reduced self discharge rates, dust and moisture resistance moves from IP22 to IP65, better battery mounting options, more batteries supported per BMS, and perhaps most importantly, the rollout of NG batteries brought the ability to combine multiple BMSs and their batteries into a single virtual battery.

Next generation batteries

NG batteries are available in 12, 24, and — for the first time — 48 volt nominal configurations. 12 volt batteries range from a 1,280 watt-hour, 100 amp-hour option to the 3,840 watt-hour, 300 amp-hour model. 24-volt batteries start at 2,560 watt-hours and 100 amp-hours and range up to 7,680 watt-hours from the 300 amp-hour model. Currently Victron only offers one 48-volt nominal battery at 5,120 watt-hours or 100 amp-hours.

All Smart NG batteries are rated for 2,500 cycles at 80-percent depth of discharge and 5,000 cycles at 50-percent. Victron rates all the batteries for 1C continuous charge and discharge and, for most of the line, 2C for 10 seconds of pulse charge or discharge current. The 12v/150ah, 12v/300ah, and 24v/300ah support 1.5C pulse charging. With 12 and 24 volt batteries, each BMS supports a maximum of 50 batteries connected. With 48 volt batteries, the per BMS limit drops to 25. Each GX system supports up to 5 NG BMSs. If I understand the limits correctly, that means a single GX instance could support up to 250 batteries and 1.9 megawatts of storage capacity. I don’t foresee marine or mobile installations pushing those limits.

Next generation BMSs

Victron offers a total of four NG BMSs. From smallest to largest, the lineup includes the SmallBMS NG, VE.Bus BMS NG, Lynx Smart BMS NG 500 A and Lynx Smart BMS NG 1000 A. The smaller two, out of the box, won’t meet ABYC E-13’s requirements for a BMS controlled disconnect device. However, they do have allow to charge and allow to discharge terminals that could be used to control an external relay or contactor to meet the requirement. In contrast, the Lynx Smart BMS NGs feature built in contactors to meet all ABYC requirements and enable the safest possible installations. The 500 amp Lynx NG BMS supports 500 amps continuously and surge current of up to 600 amps for five minutes. The 1000 amp model supports 1,000 amps continously and up to 1,200 amps for five minutes.

Both sizes of Lynx Smart NG BMSs feature a pre-charge resistor. As the name implies, they pre-charge capacitive loads like inverters to minimize high-current inrush when the contactor closes. The pre-charge functionality is automatic and likely occurs without any user awareness. Additionally, all the NG BMSs utilize allow to charge and allow to discharge contacts. These contacts change state when the BMS determines the battery should no longer be charged or discharged. The contacts are not needed for charge and discharge devices that communicate via a GX device. However, the contacts enable control of other non-communicating sources including older Orions and non-Victron branded equipment.

Victron batteries come at a premium compared to many of the value oriented batteries in the market. Each battery bank needs a BMS. The Lynx Smart BMS 500 NG has a minimum retail price (MRP) of $803.25 and the 1,000 amp model has an MRP of $1,071. NG batteries range widely in price based on capacity. At the lower end, the 100 amp hour, 12 volt battery has a $973.25 MRP. On the high end of capacity, the 300 amp hour, 24 volt battery weighs in with a $3,933.80 MRP.

Lets compare to some other batteries out there:

Description	Battery cost	BMS/Hub Cost	Watt-hour capacity	$/watt-hour
BattleBorn 100ah 12v Smart	$899	$149	1,280	$              0.82
BattleBorn 270ah 12v Smart	$2,299	$149	3,456	$              0.71
Epoch 460ah V2 Elite 12v	$2,199	$0	5,888	$              0.37
Epoch Essentials 105ah, 12v	$499	$0	1,344	$              0.37
Epoch Essentials 460ah, 12v	$1,499	$0	5,888	$              0.25
Lithionics 630ah 12v	$8,923.95	$0	8,064	$              1.11
LiTime 280ah 12v Smart	$609.99	$0	3,584	$ 0.17
Mastervolt Mli 12/6000	$6,088.26	$0	6,000	$              1.01
Victron 1x100ah 12v	$973.25	$803.25	1,280	$              1.39
Victron 2x200ah 12v	$2,966.5	$803.25	5,120	$              0.74
Victron 4x100ah 12v	$3,893	$803.25	5,120	$              0.92
Victron 4x300ah 24v	$15,735.2	$803.25	30,720	$              0.54

As you can see, Victron isn’t going to be the least expensive option out there. In fact, large lower cost batteries, like the Epoch Essentials and LiTime batteries, are dramatically cheaper. However, no other battery in this list delivers the features and capabilities of the NG batteries. In fact, although it makes sense to evaluate the options, comparing these batteries to a simple drop-in battery without Victron comms is a stretch.

Paralleling Lynx BMSs to create virtual batteries

With the introduction of the NG series of batteries, Victron added the ability to parallel BMSs and create virtual batteries. Virtual batteries combine multiple strings or banks of batteries — with each bank controlled by its own Lynx BMS — into one logical battery. The virtual battery represents the total of all paralleled banks.

During normal operations, the main difference with virtual batteries is the rolled up reporting displayed for the virtual battery. Virtual batteries allow mixing of both Lynx Smart BMSs and Lynx Smart NG BMSs. However, Smart batteries need to be behind a Smart BMS and NG batteries behind a Smart NG BMS. Additionally, you can only combine BMSs with the same current handling ratings.

As the table above shows, the system supports numerous options for the individual strings of batteries behind each BMS. Additionally, there is no requirement that the total capacity behind each BMS be balanced. So, you could parallel a 24v, 1,200 amp hour string behind one BMS with a 24v, 200 amp hour string behind another. As probably goes without saying, voltage must match across all BMSs.

At first glance, you might be thinking that parallel BMSs and virtual batteries is just a reporting nicety and doesn’t change functionality. During normal operations, there’s some truth to that. But, when things go wrong or get complex, parallel batteries really shine. Victron has written extensive logic to ensure safe combining and separating of BMSs and their batteries. If a BMS and its associated batteries disconnect from the DC system — whether automatically because of a fault or manually by operator intervention — the system manages the disconnection and reconnection. When a bank is removed, the system reduces the ratings on the virtual battery to reflect the new capacity. When the removed bank is ready to rejoin, it waits until voltages are safe to recombine them.

Dynamic DVCC

Victron’s DVCC, or distributed voltage and current control, allows battery BMSs to communicate with other components on the GX network. Via this mechanism, the batteries indicate desired charge voltage as well as charge and discharge current limits. DVCC becomes an integral component of parallel batteries.

The table above shows how various battery parameters from individual BMSs combine to set the values of the virtual battery. For DVCC, the lowest charge voltage limit from individual BMSs is communicated to charge sources. The virtual battery sums charge and discharge current limits from all connected and online BMSs.

In my test system, with one battery behind each BMS, DVCC sets CCL to 200 amps per BMS and DCL to 600 amps per BMS. The BMSs command a CVL of 3.5 volts per cell or 28 volts for a 24 volt nominal system.

The two images above show VRM’s status with one of the two physical batteries removed from the virtual battery. Essentially, all values reduce by 50 percent but operations continue normally. The online battery is at 100 percent SOC in the second screenshot so the CVL calls for a float value. Although I did all my testing with two BMSs and one battery behind each BMS, this same system could scale up to five BMSs with 50 batteries behind each BMS. If resilience is a priority, like in the case of an offshore cruising boat, size the sytstem to cope with the loss of a BMS and associated batteries.

Performance

This is normally where I talk about how the various components of the batteries hold up to extreme load. I’m pleased to say this section is going to be rather boring. The only time I’ve induced anything even slightly interesting was with a loose negative connection to one of the batteries. As soon as I placed a heavy load on the system, I got an over-temperature warning. I quickly found the loose terminal, tightened it up and all returned to normal. My testing included over 200 amps load on a single BMS and attached single 200 amp hour, 24 volt battery. Although the BMS is rated for 500 amps continuous, the battery is only rated for 200 amps continuous and 400 amps for up to 10 seconds. However, I’ve never seen any issues from the batteries, even when I’ve pushed them past their ratings.

Connecting multiple BMSs in parallel

One of the challenges of tying in multiple BMSs is the location of the tie. Victron’s Lynx system bolts together and is designed to have a single BMS in the middle with battery connections on the left and loads on the right. But, what do you do when you have two BMS? You can’t chain them together side by side. So, effectively, you need to have two separate Lynx busses and tie them together. The snippet above comes from one of Victron’s reference design drawings. In it, you can see — as I’ve pointed out with the arrows — that Victron’s reccommended approach is to cable the ouput lugs of the second BMS to the distributor side of the first one.

In building my test setup, I followed the reference drawing’s suggestion and wired up the output of BMS #2 to the distributor attached to the output of BMS #1. The approach works just fine but, as you might expect, results in unequal charge and discharge rates. This makes perfect sense since the cabling paths to the two BMSs and batteries are of different lengths.

The chart above illustrates the behavior I’ve observed running the system with differing wiring resistance. The blue line is the upper BMS with its shorter wiring run and hence lower resistance. The orange line shows the lower BMS with greater resistance from its longer wiring run. Lastly, the black and purple lines represent state of charge of each battery. The discharge test began with both batteries at 100-percent SOC. As soon as the load hits, we see the upper BMS handle more load. Eventually, the lower BMS begins handling more of the load as the upper battery’s voltage sags as the SOC declines.

About one hour and 45 minutes into the load, the lower battery surpasses the upper and supplies the majority of the load. A few minutes after that, the upper battery hits the 10-percent SOC and the BMS takes over opening the contactor. Now, the lower battery and BMS handle all of the load until that battery also reaches 10-percent SOC and all batteries are offline.

At first, the potential imbalance felt problematic. However, the more I’ve reflected on it, the less trouble I see from it. In testing, I’ve seen SOC drift pretty far apart but it always comes back together during recharge. I’ve tried to force SOC further apart with some partial charge cycles but still haven’t seen any troubles. The more I’ve worked with it, the more I think it may actually provide design flexibility. With all of the management tools for multiple banks, a system designer is now free to utilize multiple battery banks throughout the boat. The system will manage itself and maintain safe operations even as SOC potentially drifts during normal operations.

If this imbalance is problematic, there is a relatively easy solution. Rather than connecting using a distributor connected directly to one BMS, the distributor could be remote to both BMS. Then, equal length wires can be employed to connect both BMSs to the distribtor.

Managing BMS reconnection

In allowing multiple BMSs’ output to be combined, Victron also has to manage the combination and separation of the batteries to ensure safety. If the batteries are combined with too large of a voltage delta, there is a potential to create unsafe conditions. If the voltage delta is too large, very large amounts of current may flow between the batteries. This energy flow could exceed the current handling capabilities of numerous components in the system.

Victron ensures this doesn’t happen by not allowing the BMSs to combine unless their voltages are close enough to ensure safety. It appears Victron has determined the safe delta is a little under one volt. In my experimentation, I’ve created larger deltas and watched the system wait in a pending state for as long as is needed to combine batteries safely. It’s worth noting that it’s possible for a battery to remain pending for a very long time, potentially many hours, if the batteries don’t get close enough in voltage.

Tearing it all apart

Because Victron uses an external BMS, the battery teardown happens in phases. The first phase simply involves taking the covers off the Lynx components. With the cover off, much of the BMS’ innards are easily on display.

In some respects, contactor based BMSs are simpler. There aren’t rows of MOSFETs for charge and discharge control. Instead, there’s a single, very large contactor in the positive current path. On the 500 amp BMSs I have, the contactor handles 500 amps continuously and 600 amps for up to five minutes. Victron uses a temperature sensor on the positive bus bar to ensure temperatures stay within a safe range. The negative bus bar is actually a shunt with calibrated resistance across it. There are two small cooling fans that I’m yet to hear run, even when pushing pretty large loads.

Opening the batteries is easy, except for the aluminum nuts used to secure the positive and negative terminals into the case. I think the thread must deform when they’re tightened to the posts. I had to really haul on them to get them off and wasn’t able to rethread them back on. In some of the closes-ups, you will see the damage to the thread on the posts.

Once inside, the batteries are pretty simple. There are a total of 16 cells in a 2p8s arrangement. Each cell is 100 amp hours at 3.2 volts nominal. Each cell two-parallel cell pair has a cell management module connected. From what I can tell, the module manages balancing and reports on cell voltage and temperature.

With the NG series, Victron moved from analog communications between BMS and battery to digital. Cabling remains the same, so previous battery to BMS extensions can still be used. Digital communications enables the exchange of more parameters over the same 3 wire connection.

Interestingly, the outer most busbars both also serve as shunts. The cell management modules on these bus bars are different colors and have wires connected to their shunt terminals, unlike the other six modules. The black and white wires are shunt leads connecting between the bus bar, which must have a calibrated resistance, and the cell management module. The non-Lynx BMSs rely solely on these shunts for current measurements from the batteries.

Despite a good scan of the QR code, I have not been able to decode the cells’ QR codes to determine manufacturer or other information. I have run across this more and more frequently in recent reviews. I can’t draw any conclusions about what it means. It seems unlikely that Victron is cutting corners with cells but without the ability to look them up I simply don’t know.

Final thoughts

Victron’s NG batteries are a formidable energy solution. The introduction of parallel BMS functionality affords a lot of design flexibility to deliver large, robust, and efficient energy systems onboard even the largest of boats. But, as the table at the start of this article shows, those capabilities come at a cost. This is not a cheap system, although the costs do get more reasonable as you scale up the number of batteries behind a BMS. For those boats with simpler needs, there are many compelling options available at lower cost. But, for larger cruising boats operating beyond site of land, the design flexibility and robustness of Victron’s current solutions are tough to top.