Loss of battery power

[Amocat07]

At 70-100% charge, my radcity 5 plus standard frame has no problem going up 300' fairly steep hill to my driveway.  Can reach 9 - 11 mph, in 3rd gear and cadence of 60-80.  Came home this AM, battery showed 30% and bikes max speed was 4-5 mph in 2nd gear and cadence easily 100. Does that seem right to anyone?

[JimInPT]

At 70-100% charge, my radcity 5 plus standard frame has no problem going up 300' fairly steep hill to my driveway.  Can reach 9 - 11 mph, in 3rd gear and cadence of 60-80.  Came home this AM, battery showed 30% and bikes max speed was 4-5 mph in 2nd gear and cadence easily 100. Does that seem right to anyone?

I don't know about the City 5+ specifically, but as I recall Rad programs its controller to reduce maximum power to the motor, to a more-efficient operating level, once the charge level gets down to the range where you had a problem, in an effort to provide max range at lower power to hopefully make it back home.  So I'm thinking what you observed is within spec.  One way to test that is to make the uphill ride at 70% charge or higher and note the maximum wattage on the display, then repeat exactly the same but with a 25-30% charge level; I believe you'll see a lower maximum wattage as the controller programming throttles it back.  "Slower, but further" seems to be the design goal near the end of the charge.

I never let my MiniST2 get below 3 bars without putting it on the charger - if it hits 2 bars it's charged back up; this battery chemistry operates best and for maximum charge cycles when operated between 20-80% and I wouldn't go below 25% ever, unless it was at the tail-end of an unexpectedly-draining ride.  They don't have a "memory" like old NiCd cells used to have, but they do need a little TLC for routine charging and usage.

[Amocat07]

Makes sense, thanks for the insight.  I'll run the test later this week and note the power.

[Radio Runner]

Its not totally just so you can get home so to speak. Lithium Ion batteries can fail permanently if discharged 100%. What's most likely  happening is the BMS (battery management system) is kicking in to save your battery from to much voltage loss and catastrophic failure.

[DickB]

The controller will limit power when the SOC (State Of Charge) diminishes to about 20% (two bars).

[DickB]

Its not totally just so you can get home so to speak. Lithium Ion batteries can fail permanently if discharged 100%. What's most likely  happening is the BMS (battery management system) is kicking in to save your battery from to much voltage loss and catastrophic failure.

The BMS does not limit current. I either enables it 100% or shuts it off completely.  The controller limits current at low SOC (State Of Charge).

[Radio Runner]

Its not totally just so you can get home so to speak. Lithium Ion batteries can fail permanently if discharged 100%. What's most likely  happening is the BMS (battery management system) is kicking in to save your battery from to much voltage loss and catastrophic failure.

The BMS does not limit current. I either enables it 100% or shuts it off completely.  The controller limits current at low SOC (State Of Charge).

Interesting, that's not my experience with LiON battery use in other hobbies. Can you also explain the graph a bit more since it starts out at 54V and Rad Batteries are 48v?

[DickB]

Nominal voltage of the cells is 3.6 - 3.7V (depending upon manufacturer) which rounds to 48V for 13 cells in series. Charge float voltage is 4.2V per cell or 54.6V for the battery, which is the float voltage of the Rad charger. Cells will sag a bit in voltage after they come of the charger.

The graph is a real-world test of my 2021 Rad Rover battery. I ran throttle only wide open on flat roads, stopped every two miles and read voltage after a 60 second rest.  I increased the top speed which the controller then throttles to about 24.5 mph. Watts ranged from 740 ish to 680 until the controller started limiting current as evidenced by the watt reading dropping. To calibrate the battery meters, I replaced the batteries with a variable power supply and recorded the voltage at each transition from bar to bar.