LiTime self discharge test

[s/v Jedi]

Hi,

I just did a 7-week long discharge test on a LiTime 48V 100Ah battery. When I put it in storage it was at 59% SOC. I used the app to switch it off but also disconnected the negative battery terminal to make sure.

7 weeks later I reconnected the negative battery terminal, switched on the charger which turns the battery back on and the app reported 46% SOC.

So the battery lost 13% in 7 weeks so let’s say 2% per week to stay on the safe side.

I don’t know if 24V and 12V batteries have the same self discharge but I would guess so.

This discharge is mostly caused by the BMS that never switches off.

This is the battery and charger I have: https://www.litime.com/products/48v-...rt-battery-kit

[Downeaster]

I just checked 3 of my LiTimes. After 5 weeks of storage there has been no self discharge so far. However they are brand new and were also switched OFF using the LiTime app.

The three are this 12v model: https://www.litime.com/products/12v-...arting-battery

I’m going to leave them on for a couple weeks and see then. I haven’t heard that fast discharge is an issue with LiTimes.

[Hughesfamily]

I have the Litime Trolling Motor 100Ah cold temperature protection. I am constantly checking the battery monitor. I have seen only very small 1% self discharging numbers over 2 to 4 weeks. I will be storing it here very soon for a bit. I’ll note the discharging.

[s/v Jedi]

Originally Posted by Downeaster

I just checked 3 of my LiTimes. After 5 weeks of storage there has been no self discharge so far. However they are brand new and were also switched OFF using the LiTime app.

The three are this 12v model: https://www.litime.com/products/12v-...arting-battery

I’m going to leave them on for a couple weeks and see then. I haven’t heard that fast discharge is an issue with LiTimes.

How can you see the self discharge when they are switched off? You first have to switch them on using a charger, then reconnect the app with Bluetooth and only then will it update the SOC percentage.

[s/v Jedi]

Originally Posted by Hughesfamily

I have the Litime Trolling Motor 100Ah cold temperature protection. I am constantly checking the battery monitor. I have seen only very small 1% self discharging numbers over 2 to 4 weeks. I will be storing it here very soon for a bit. I’ll note the discharging.

Unfortunately we use the golf cart so often that I can’t get self discharge numbers for when it’s switched on.

I also have a trolling motor model but I think it’s only 20Ah at 24V. It’s been in use during these 7 weeks to keep the boat running but the big batteries will come online soon and then I can test that battery too.

I find the self discharge higher than expected but maybe it’s higher for 48V batteries. This battery is brand new as well, has only done two cycles.

[Downeaster]

Originally Posted by s/v Jedi

How can you see the self discharge when they are switched off? You first have to switch them on using a charger, then reconnect the app with Bluetooth and only then will it update the SOC percentage.

Correct - that’s what I did to check them. And note my data so far is for a pure storage situation (e.g. over winter with zero loads or charging).

[s/v Jedi]

Originally Posted by Downeaster

Correct - that’s what I did to check them. And note my data so far is for a pure storage situation (e.g. over winter with zero loads or charging).

Then that is amazing because they should at least self discharge some. When you don’t measure any self discharge then maybe the batteries are so new that they did not calibrate SOC settings yet. For example, the battery I am testing started telling me the charger would take 48 hours to charge the battery while it was only 7-8 hours.

This battery I test is new and working great so I’m pretty sure it’s fine.

[Downeaster]

Originally Posted by s/v Jedi

Then that is amazing because they should at least self discharge some. When you don’t measure any self discharge then maybe the batteries are so new that they did not calibrate SOC settings yet. For example, the battery I am testing started telling me the charger would take 48 hours to charge the battery while it was only 7-8 hours.

This battery I test is new and working great so I’m pretty sure it’s fine.

Could be... Not sure how the LiTime BMS calculates SoC. I guess to do this precisely and conclusively we would need to compare resting voltages over time.

[s/v Jedi]

Originally Posted by Downeaster

Could be... Not sure how the LiTime BMS calculates SoC. I guess to do this precisely and conclusively we would need to compare resting voltages over time.

Yes, unfortunately I failed to record voltages before and after the 7 weeks

[Panope]

We recently installed Epoch 460ah batteries in a customer's boat. The owner was frequently monitoring SOC with the battery's blue tooth app, however the battery system was seeing very little use for several months.

At some point, with an indicated state of charge of greater than 50%, both batteries shut themselves off due to low voltage.

We eventually determined that the built in amp counter was not measuring small parasitic and self discharge currents, and therefore giving wildly inaccurate SOC readings.

The owner is now using voltage to double check state of charge during periods of inactivity.

[jcapo]

Originally Posted by Panope

We recently installed Epoch 460ah batteries in a customer's boat. The owner was frequently monitoring SOC with the battery's blue tooth app, however the battery system was seeing very little use for several months.

At some point, with an indicated state of charge of greater than 50%, both batteries shut themselves off due to low voltage.

We eventually determined that the built in amp counter was not measuring small parasitic and self discharge currents, and therefore giving wildly inaccurate SOC readings.

The owner is now using voltage to double check state of charge during periods of inactivity.

The JBD BMS in the Epoch 300AH batteries does not measure current below about 500ma. From what I have read the same applies to many other drop-in batteries.

[wholybee]

Originally Posted by s/v Jedi

Hi,

I just did a 7-week long discharge test on a LiTime 48V 100Ah battery. When I put it in storage it was at 59% SOC. I used the app to switch it off but also disconnected the negative battery terminal to make sure.

7 weeks later I reconnected the negative battery terminal, switched on the charger which turns the battery back on and the app reported 46% SOC.

So the battery lost 13% in 7 weeks so let’s say 2% per week to stay on the safe side.

I don’t know if 24V and 12V batteries have the same self discharge but I would guess so.

This discharge is mostly caused by the BMS that never switches off.

This is the battery and charger I have: https://www.litime.com/products/48v-...rt-battery-kit

Were you able to tell how much if at all the cell balance changed? I.E., was the self discharge rate the same between cells? AFAIK, that is the best way to know if cells are matched, by performing a long self discharge test.

[wholybee]

Originally Posted by Panope

We recently installed Epoch 460ah batteries in a customer's boat. The owner was frequently monitoring SOC with the battery's blue tooth app, however the battery system was seeing very little use for several months.

At some point, with an indicated state of charge of greater than 50%, both batteries shut themselves off due to low voltage.

We eventually determined that the built in amp counter was not measuring small parasitic and self discharge currents, and therefore giving wildly inaccurate SOC readings.

The owner is now using voltage to double check state of charge during periods of inactivity.

This typical of BMS integrated SOC meters/coulomb counters. It is because the BMS doesn't have a physically large shunt to measure current, but instead use a hall effect sensor. Small currents to not register accurately. I experience the same thing with my JBD BMS, but my Victron BMV-712 is quite accurate over a long period.

[s/v Jedi]

Originally Posted by wholybee

Were you able to tell how much if at all the cell balance changed? I.E., was the self discharge rate the same between cells? AFAIK, that is the best way to know if cells are matched, by performing a long self discharge test.

Unfortunately the LiTime app does not show balance details, only if everything is okay or not and if it is balancing or not.

It did balance, but it does so every time it is fully charged. When you don’t know the maximum deviation in cell voltage, this is useless.