Cub Cadet LT42e battery testing or replacement options?

[UrrgLak36]

TLDR:
- Is there a way to test, balance or recalibrate the batteries for the mower ?
- Can one do a swap to a 60-100ah LiFePO4 golf cart battery rather than trying to find a pricy CubCadet replacement?

Ok, I realize that batteries degrade and I have run this ZT42e very hard for almost 5 years mowing my lot, daughters and helping out my parents. Running this easily 4 or more days a week. So, over the years I have seen the runtime dip a little. But about a couple months ago, the mower drastically changed.
1) big runtime loss mid summer as runtime (on eco mode) is around 50-60% now compared to new
2) It used to run to about 5-6% then just cut the blades off and I could drive to the trailer and go home. But now around 28% the whole thing just dies and you can hear to contactors open with all power lost and control pad dead and the blades slowly spin down over like 20-30 seconds. I can then pull key and put back in and it will be at 0%, but I can drive it to the trailer like before and head to the charger.
3) I have also noticed that while charging, when it gets into the mid 80%'s, it will just jump to 100% and be done.

So, I am thinking that possibly one of the two 30ah batteries in there is imbalanced, weak or dying, so when its voltage drops down the mower is just shutting off. Then on charging either the weak one is reaching the point it will no longer charge and stops the charging session or the good one is actually at 25-30% and is reaching the voltage cutoff before the other one and stops the charging. Not really sure.

I dropped it off at the local Cub Cadet dealer to look at. I don't think service shops have any clue what to do with these electric mowers. They had it about a week and returned it saying runtime was within spec for the age. But they could replace the batteries for me if I wanted.

They want just over $2000 PER BATTERY!!! Wow. I have no clue where they are sourcing them from as I cannot find them in stock anywhere online myself. And online they are still showing around $1800 for a 30ah battery. Dang?

Here is what I am thinking are some possible options:

1) disconnect the batteries and only hook one up at a time and try charging them independently see if they are just imbalanced?
2) Possibly charge them independently on my bench lithium charger? Have to find their proper voltage cutoff first. Hope that is printed on them.
3) Is there any sort of battery recalibration that can be done on these?
4) Purchase 1 or 2 battery replacements? Anyone have a good place to source them from at a reasonable cost?

Or, would these lawn mowers accept a golf cart lithium battery? I converted my side by side to Lithium and that has been great. Wondering if I can drop another of those in the back of this and have it work with the mower? I could unhook and charge with one of my other chargers if the included one doesn't like LiFePO4. Wonder if a 100ah would fit in there. The extra mowing time would be nice.

Thanks for any input or ideas.

 

[Jviv]

I too have been searching for these answers. Has anyone found any options on how to trick the system into thinking an aftermarket battery is supposed to be there

 

[Mekanix]

Unfortunately you cannot simply install another set of batteries in these units. Each battery pack contains a BMS that communicates with the VCM over the CAN bus, and if that communication is missing the VCM will not enable the system or allow charging. Trying to bypass that protection is difficult, because it would likely require reading the CAN bus wake signal and then spoofing that signal so the controller believes the BMS is present. I am also curious whether anyone has successfully replaced the motor controllers and built a fully DIY control system instead. The cost of replacement batteries is extremely high, especially in situations where the packs themselves may still be usable but the BMS will not wake up to allow charging.

 

[UrrgLak36]

Dang...computers. Well that is out of my reach. Was hoping that I would just need to match the voltage with something like my golf cart batteries. Even if I needed to charge it manually with the LiTime charger. Then get the added bonus of a 100ah battery.
But, I did pull both batteries and checked on them individually and found one was not charged all the way. I wonder if the way they are wired in parallel if they are not charging and discharging in sync. Similar to home batteries without bus bars or correcly sized wiring.
When this season starts, I will charge them up individually with my Lithium bench charger and put them back in, but swapped positions and see if that helps get some more consistency out of them.

 

[Mekanix]

Dang...computers. Well that is out of my reach. Was hoping that I would just need to match the voltage with something like my golf cart batteries. Even if I needed to charge it manually with the LiTime charger. Then get the added bonus of a 100ah battery.
But, I did pull both batteries and checked on them individually and found one was not charged all the way. I wonder if the way they are wired in parallel if they are not charging and discharging in sync. Similar to home batteries without bus bars or correcly sized wiring.
When this season starts, I will charge them up individually with my Lithium bench charger and put them back in, but swapped positions and see if that helps get some more consistency out of them.

The battery packs on these are wired in parallel, so you’re really just increasing runtime, not voltage.
The bigger issue you’re likely running into is the BMS inside each pack. Even if you try to bench charge them, the BMS may already have locked things out if it sees the pack is out of balance.
Inside each battery there are a lot of individual cells grouped into modules, and the BMS is constantly monitoring those. If one module is even slightly out of balance, say around 0.2V or so compared to the others, the BMS can prevent charging altogether.
In theory, the packs should attempt to self-balance over time, but I haven’t personally seen that happen reliably in these units.
I wouldn’t recommend opening the batteries up. There’s a lot going on inside, and it’s easy to cause more issues than you fix.