With a properly wired and cared for LiFePO4 system this never should have been allowed to happen. The most painful element of this whole debacle is that when the owner purchased this battery in 2010 it cost him approx $9800.00. To treat a 10K battery like you would a $65.00 Wal*Mart lead acid battery, heck you might as well go to Foxwoods and hand over your dough to the Tribe... Sadly this owner followed the instructions and still had a failure. How & why??

These cells should never get below 2.7V in normal service and with a good BMS. With a properly wired system, they should never dip below 2.9V per cell. The manufacturer suggests that anything below 2.0V to 2.5V causes "irreversible cell damage".

When I dug into the battery I discovered that nearly every bolt holding the busbars to the battery terminals had become loose. The negative "S" shaped bus bar was so loose it literally wiggled up & down freely.

Once the case was apart I discovered that the lower three-quarters of all the cells were bulged & swollen. The only cell compression was via that one gray colored sheet metal bar near the top of the case. The gray metal plate behind it, with two vertical ribs, is not physically attached to the bottom of the case and is literally free floating. Nearly all LiFePO4 prismatic cell manufacturers require full compression end plates of the cells.

The case design on this $10,000 battery simply does not satisfy a cell manufacturers requirement for adequate cell compression, especially if your design includes regularly pushing the cells into the dangerous upper-knee. This design lapse, and I can say that because Mastervolt has admitted to me & recognized this was an issue, allowed the lower bout of the cells to bulge outwards when being charged at 14.6V, and then that voltage held/maintained there for far too long.

"But RC the cell maker suggests up to 4V per cell is safe and 3.65VPC is a good charging voltage?"

Let's stop for a minute and discuss the three things that are misleading about most LFP cell makers specification Sheets;

Max safe voltage - Maximum brief safe voltage for the cell
Max Constant Voltage DURATION - Rarely if ever specified or discussed
Charge Current as related to Ah capacity and Considering CV DURATION - Yet to see this in any specification sheet.

Misunderstanding #1: "These cells can't be fully charged until 3.65V / 14.6V or in this case 29.2V".

This statement is actually untrue. I can charge LFP cells to the same exact Ah capacity, (tested using lab grade equipment) as I get at 3.65VPC / 14.6V at just 3.4125VPC / 13.65V. The only difference being the CV (constant voltage) duration. I have tested this repeatedly on numerous cells including multiple brands of prismatics (LiFePO4 & LiFeYPO4), and 18650 LiFePO4 cylindrical cells. All of these cells can be charged to 100% Ah capacity at just a tick over 3.4V the only difference is we can now hold the CV duration longer if charge current is in the .3C range. With very low charge current the battery is near fully charged as the voltage approaches 3.4125VPC and the CV duration is extremely short even at this very low voltage. the rate at which you charge the cells also matters. Typically speaking if you charge to 3.6VPC you'll want to stop charging once you hit that voltage. In a perfect world you could allow the current to drop/taper to .03C at 3.6V but again we are dancing on the head of a needle at this voltage so teh safe bet is to just stop at 3.6V per cell.

Misunderstanding #2: "3.60V / 14.6V / 29.2V is perfectly safe, the spec sheet says so."

This is only quasi-true and it leaves out a lot of critical information. The critical things left out, that really matter, are charge current and the duration the constant voltage is held. What? Huh?

The max safe recommended charge voltage is not just about the target voltage with LFP. The decision on when to stop charging needs to include the charge current rate and the duration the voltage is held at the max safe level. In other words, in order to recommend a maximum safe charge voltage for LFP it must include the charge rate and the max CV duration at the charge current being used.

Lead acid charging requires multiple hours at the constant voltage target, but LFP does not. LFP can not be held for multiple hours at 3.65VPC / 14.6V / 29.2V yet this is the part that is almost always ignored when discussing LFP charging.

Most boat owners are using lead acid chargers that offer anywhere from 1 hour to 4+/- hours of CV duration or unlimited hours at constant voltage in the case of stock alternators or cheap charge sources. Holding the constant voltage duration, at the 3.65VPC that Mastervolt used to recommend, and then holding it there is what over charged and caused these cells to swell and lose considerable Ah capacity. We have tested, in our lab, 35-40 different LFP cells charged at 14.6V, using lead designed acid chargers, and the capacity is diminished rather rapidly when CV duration is held.

MAX SAFE CHARGING VOLTAGE IS A USELESS SPEC IF IT IGNORES CHARGE RATE AND DURATION AT CONSTANT VOLTAGE

What the Chinese spec sheets / manuals fail to tell you is the "rest of the story" and the rest of the story must always include:

Charge Rate & Constant Voltage maximum duration, at XX charge rate, yet it rarely does.

For example at a charge rate of .5C or 50% of Ah capacity (50A for a 100Ah battery) when charging to 3.65VPC / 14.6V / 29.2V you can only hold that voltage for a few minutes once 14.6V or 3.65VPC has been attained or we now start over-charging the cells. Repeat this on every cycle and you can kiss your investment & long cycle life you paid for bye-bye, as this owner did.

In contrast to the max CV duration at a high rate of charge, if we charge to 14.6V with a low charge rate, such as a solar system, of just .05C or 5% of Ah capacity or 5A for a 100Ah battery the cell is going to be full well before you even hit 3.65V / 14.6V / 29.2V and anything beyond this point is unnecessarily damaging/stressing/overcharging the cells.

This battery had a Mastervolt suggested charge voltage of 29.2V for a 24V bank. Holding absorption at 3.65V is what will cause the over-charging and cell swelling or bulging, like these cells suffered from. Cell swelling is considered normal in most prismatic cells and this is why prismatics need "cell compression".

The Chinese manufacturer of the cells in this Mastervolt battery insists on cell compression using "jigs & straps". The "jigs" are metal end plates and the "straps" are meta straps that join the "jigs" and keep the cells in compression so case swelling can not occur during normal use.

If you know me you also know I believe any voltage over 14.2V is simply unnecessary for a marine house bank and 14.2V is using a "stop charge" protocol meaning when it hits 3.55VPC / 14.2V / 28.4V at .3C you simply stop charging. If using a low charge rate the stop point would be a bit lower than 3.55VPC / 14.2V / 28.4V.

Interestingly enough, Mastervolt now recommends 14.25V or 28.5V as the new "recommended max charge voltage". This may help minimize cell swelling, due to chronic upper knee charging and over absorbing, but is still a bit on the unnecessarily high side, especially if you are using charge equipment designed to hold the CV duration..

When the Chinese cell makers, Winston/Thundersky in the case of this Mastervolt battery, say 3.65V per cell is okay this means it is "okay" to charge to 3.65V then STOP CHARGING. This does not mean to charge to 3.65V then hold that voltage for an "absorption period" like typical lead acid charge products do. it also fails to include for low charge rates and the over charging it can create..

Charge to XX.XX volts and stop is NOT how any of the CC/CV charge sources we use in the marine environment operate. To get around this and keep our cells safe from over-charging we can lower the CV charge voltage and adjust the absorption duration to as short as you can so as to not over charge the cells or to hold them in teh upper knee range any longer than is absolutely necessary.

In my experience, which I gained through actually bench testing of LFP cells, the Mastervolt engineers should have picked up on this far sooner than they did. Today, a bit too late in my opinion, many LFP makers are finally recommending lower charge voltages, including Mastervolt.

If you move back two images you can see the cell compression bar holding the upper quarter of the cell. It seemed to do its job up high but there was nothing holding the cells in compression for the lower three quarters of the cell.

When the BMS allowed the cells to over-charge, at 3.65V per cell, this is exactly what can be expected. Seeing how bulged these cells were it is not a surprise at all. Charging at 3.65V per cell is just unnecessary and can certainly be damaging to your expensive investment.

Thankfully Mastervolt has now reduced the maximum recommended charging voltage to 3.55V per cell or 14.2V. In my experience & opinion this is a slightly better and certainly safer voltage but still unnecessarily damaging to the cells when coupled with multiple lead acid charge sources such as alternator, solar, wind, hydro gen, battery chargers or hydrogen fuel cells that may lack adequate LFP control functionality.

Please understand that it is not the 3.65V per cell that damages them, it is the lead acid "absorption cycle duration" that is simply held too long that causes this damage. If you could 100% ensure that every cycle would charge until the cells hit 3.65V, then the charging 100% stopped, this would be okay. Unfortunately this is not how the devices currently available operate or function with the exception of a very select few.

Here's the Thundersky logo on the internal cells. Everything inside the battery & BMS was actually pretty robust and even the copper busbars were tin plated. This is excellent. Unfortunately the torque on each busbar was really far too loose, and the battery case Mastervolt used during this vintage, did not allow for an individual to easily check the terminals for proper torque.

When I conversed with Mastervolt about their self discharge claims, which coincidentally were identical to the Thundersky documentation for bare cells, they admitted they had no idea what the quiescent draw (phantom load) of the massive BMS on this battery actually was? On this vintage battery there was no possible way to shut down the BMS or isolate it from the cells, so the 3% self discharge claim per month was, in essence, grossly inaccurate because it was based only on bare cells and not inclusive of the BMS's quiescent load.

How on Earth can you sell a $10,000 battery, and make a self discharge claim (based on bare cells) without knowing the actual parasitic draw of your own permanently mounted BMS? Seems odd but things can tend to get looked over.

WARNING:

DO NOT open a Mastevolt LFP battery of this vintage and remove the BMS from the cells. Mastervolt claims they programmed in a self destruct mode into this BMS. This process is kept so super secret that they won't even disclose how to disconnect the BMS safely.

The Debacle:

All I wanted was to order new cells for the battery and get this back up and running. Mastervolt did not even offer replacement cells nor would they sell them to us. We could easily have purchased them elsewhere, but chose not to because the basic design was so fraught with issues, I decided it was simply throwing good money at bad to invest in new cells.

Mastervolt also refused to warranty any part of this battery for the customer, which BTW was installed with a COMPLETE Mastervolt system, though I do recognize it was beyond warranty. However, as the customer stated, Mastervolt made pretty bold claims about cycle life which failed to come anywhere close to a reality due to the inherent design and voltage guidance. Frustrating to say the least.

Still, with an out of warranty battery, they could have at least explained how to disconnect the BMS so it would not "self destruct". In the end I decided it was not worth throwing money at this design so the battery was simply scrapped.

Here is the lower case and the 8 cells with the BMS system removed. The case is quite elegant in design and aesthetics but the solid points ended there. Sadly it lacks any solid measure for cell compression and considering the cells bulged, right where the compression was lacking, lends to credence to the cell compression bar up top actually doing its job. Mastervolt fully admitted to me, in writing, that this was a design flaw.

It is also painted steel which means it can rust and this battery case did have multiple rust spots despite no signs of salt water intrusion.

For what it is worth these prismatic cells cost me about $224.00 each, or about $1780.00 for eight of them, but that is just the bare cells. Mastervolt had to design this, engineer it, build and include a very hardy BMS which includes cell temperature monitoring probes, an excellent safety feature, communication, balancing and build the case then sell it through retail channels and warranty it with everyone along the way wanting to make a buck on it. If you want to understand why LFP is expensive look no further than nearly $1800.00 worth of LiFePO4 cells to make a 24V 160Ah battery.

Design Issues:

Do you really get your money's worth with a $10,000 factory engineered LFP battery? In the 2010-2011 vintage, with Mastervolt, I would say they had some improvements to make.

Issues:

Loose Bolts - All bolts interconnecting cells, BMS and busbars were physically loose, some less than finger tight. VERY SCARY! You also have NO ABILITY to check or re-torque them. One was so loose the basbar was physically rattling between the battery terminal and washer. Mastervolt claims to have addressed this in newer models.

Lack of Cell Compression - The manufacturer of these cells requires adequate cell compression in the form of solid end plates. The end plate design on the battery was essentially free floating for the bottom 2/3 and the cells bulged and were destroyed in the bottom 2/3 of the cell case. Mastervolt claims to have addressed this in newer models.

Over Charging - Mastervolt suggested charging these cells at 3.65V per cell back in 2010. This is MURDER if using typical CC/CV charging sources where absorption voltage is held at 3.65V per cell. This charge guidance, mixed with a CC/CV charge source with timed absorption, is likely what caused the cells to bulge and become ruined. Mastervolt has marginally addressed this in newer LFP batteries with a recommendation of approx 3.55V per cell. IMHO this voltage is still unnecessarily high and with too long an absorption could still lead to bulging and ruined cells.

Over-Discharging - You simply can not make a claim on "self discharge" based on the manufacturers bare cell rating and then stack a massive BMS directly bolted to the battery cells, with no on/off switch, and not know the quiescent draw of the BMS. This is a HUGE FAIL! This is what finally put the nail in the coffin for this battery, though based on cell bulging it had already been destroyed by over charging. It had been physically disconnected from the boat and it DID NOT survive the self discharge duration in the manual without murdering itself. Mastervolt claims to has reportedly addressed this in newer models with a way to shut down the BMS when the batteries are left idle.

Sealed Super Secret Case - The case of this battery is so super secret sealed that you can not even check for proper bolt torque. This is simply UNSAFE. I know Mastervolt probably does not want folks seeing Winston / Thundersky cells in there for $10,000 but in reality this is a simple safety issue.

Inferior Plastic - When I got this battery both lifting handles were broken and this was not from shipping. Mastervolt had no replacements as of May 2016. Mastervolt claims to have addressed this in newer models.

Painted Steel Case - Really?? Seriously?? This was is a $10,000 battery back in 2010 and the case was light gauge painted & stamped steel? It was already beginning to rust in numerous locations. Really painted steel for a marine battery..?

Self-Destructing BMS - I can understand Mastervolt's apprehension to allow folks to work on these batteries but when you fail to support a product, that is not even 5 +/- years old, with only a few hundred cycles on it and claims of 2000+ cycles, you could at least tell a qualified technician how to do it.

Mastervolt refused warranty, and yes I know it was technically out of warranty, but this battery failed due to engineering failures. Engineering failures including a very, very misleading self discharge claim, not even knowing the BMS's quiescent draw, charge voltage guidance, lack of cell compression, loose busbars etc.. If the BMS had not been "self destructing" I could have very easily balanced new cells and then reassembled this battery, in about two hours, with brand new Winston cells. This is really quite off-putting for such an expensive product.

Please Consider This Before You DIY:

I understand LiFePO4 technology was relatively new in 2010-2011, but if you think you can DIY a proper system, without adequate research, please take the time to understand that even a very good & experienced company like Mastervolt made numerous mistakes, in numerous aspects, on this LFP battery.

IMPORTANT: Today the Mastervolt LiFePO4 batteries are far better engineered and all the noted issues have been dealt with. I would have no qualms recommending a Mastervolt LFP battery. Please understand this battery was built in the very early days of LiFePO4. Yes, Mastervolt was one of the early Pioneers of LFP, and they certainly got some arrows in the back. Like any good company they learned from their mistakes and moved forward. Kudo's to Mastervolt for recognizing this and addressing it.