Caution for Big Battery Badger systems

[NITF]

Had installed a couple Big Battery 48V Badger units for my mother's golf cart to save her the hassle of dealing with water levels etc. once my father passed away. I had been happy with their overall performance but ran into an issue when the cart went unused for a while and when I checked on it the batteries were well below their advertised low voltage cutoff (26.6V vs 36V) level but the BMS had still not kicked in yet.

Returned the batteries for testing and was told they were fine with no explanation for the behavior so I returned them again and was just informed that unless the BMS has a minimum draw of 3A the low voltage cutoff is not enabled. Because these are small packs you have to use at least 2 in parallel so that means anything below 6A will bypass the low voltage safety of the BMS. This seems to be a terrible design because even if you had old halogen headlights/taillights you wouldn't cross the 288W minimum load for the BMS to do its job and battery damage would result if the headlamps were left on accidently.

Will definitely be checking out other solutions in the future that do not have this vulnerability due to the intermittent nature of this cart's use.

 

[sunshine_eggo]

Had installed a couple Big Battery 48V Badger units for my mother's golf cart to save her the hassle of dealing with water levels etc. once my father passed away. I had been happy with their overall performance but ran into an issue when the cart went unused for a while and when I checked on it the batteries were well below their advertised low voltage cutoff (26.6V vs 36V) level but the BMS had still not kicked in yet.

Unfortunately, even if the LVD worked, the BMS can continue to draw milliamps draining the battery further. This is why most commercial batteries recommend a recharge interval.

Returned the batteries for testing and was told they were fine with no explanation for the behavior so I returned them again and was just informed that unless the BMS has a minimum draw of 3A the low voltage cutoff is not enabled. Because these are small packs you have to use at least 2 in parallel so that means anything below 6A will bypass the low voltage safety of the BMS. This seems to be a terrible design because even if you had old halogen headlights/taillights you wouldn't cross the 288W minimum load for the BMS to do its job and battery damage would result if the headlamps were left on accidently.

It is likely that the battery sustained some damage, but not much. If it's something you watched in the past, you might notice voltage dropping a little lower than it used to for a given load.

The true failure is Big Battery didn't specify a recommended recharge interval and misled you by indicating "zero maintenance".

https://bigbattery.com/Manuals/Spec-Sheet-48V-BDGR-Kit-4x.pdf

Will definitely be checking out other solutions in the future that do not have this vulnerability due to the intermittent nature of this cart's use.

You will likely run into the same issues with all other solutions that claim 'zero maintenance" and don't specify a recommended re-charge interval.

This is a 12S NMC battery. I have a 23.3kWh 14S NMC battery.

While they claim a float voltage is not necessary, without specifying a recharge interval, they are wrong.

Recommend you charge/float to 47V moving forward. You will lose about 20% of your capacity at the top, but this will dramatically increase the cycle life of the battery.

In other words, you can charge to 47V and hold it there indefinitely with no consequences UNLESS the battery is hot. If storing in a hot environment, recommend floating at 42V continuously. 42V resting is about 20% charged. If you limit the voltage range between 42 and 47V, then cycle life will be further improved.

Charging per the above will maximum cycle life and prevent a repeat.

If float charging isn't an option, I would disconnect the battery from the cart when in storage and check it monthly, recharging if it drops below 42V.

 

[NITF]

Yeah, I understand that the BMS will have some parasitic draw as you mention in the likely mA range and although not a big pack even at 1.6KWh capacity it would take a decent amount of time to drag the batteries down. Whereas their BMS choice requiring 3A draw per pack for the low voltage protection to be enabled leaves the door open for an incredibly short recharge interval. Technically if I was pulling just below the 3A limit I would be in danger of under voltage due to no BMS protection in less than 12 hours from a fully charged battery.

Just seems like a poorly designed BMS as the voltage sensing circuit should be a very high impedance input so not sure why it would need >3A of load current to enable it. Only way I can make sense of that behavior would be if the BMS is pulling 3A in the voltage cutoff condition so any load less than that would actually be better than the protection mode but that again is just an indication if a poorly designed BMS.

Apart from the iffy specs the overall customer service has been quite poor with a lack of communication and numerous delays blamed on "new procedures" but taking over a month to determine that the battery is fine and they just have a large disclaimer on their BMS protection does not give me much confidence in the other aspects of their operation. Based on the favorable tear down of the RoyPow packs they will likely be my next golf cart battery.