Batteries Accept Only 85% of Stated Charge

I recently purchased a Satiator Charger from Grin Technologies. The charger is user adjustable and provides information related to the amount of charge each battery will accept in amp hours. I drained 3 lithium batteries to the point that the bike would not move and charged them fully. I used two 36V Easy Motion batteries and one LEED 24 V battery. The Easy Motion battery uses Samsung cells, the LEED uses Panasonic cells.

The Easy Motion 11.6 Amp*Hour battery that came with the Street only accepted approximately 85% of the stated capacity. This was observed with 2 different batteries, both less than 1 year old. The LEED battery had approximately the same result.

Anybody else observe this? Other rechargeable batteries, eg AA Eneloop NiMH batteries typically exceed the stated capacity when new. Somewhat surprising to see that these Lithium Ebike batteries don't accept the stated capacity.
 

Nirmala

Active Member
I know that electric/hybrid car manufacturers do not charge the battery to 100% as that shortens the battery's lifespan. Maybe there is something like this going on.
 

JoePah

Well-Known Member
Unless you tried charging a brand new battery with this charger, you don't really know if you have a problem or not.

My guess is that even at the Battery LVC cutoff, which is where you drained your batteries, there is still 15% battery energy remaining. The BMS protects the battery from becoming fully discharged.

Other possibilities when battery packs not reaching their full capacity are battery degradation after a year (10% a year is normal), or the battery cells didn't meet their original specs.
 

Jonah

Member
Has anyone used the satiator with a Stromer St2? If so, would you mind describing your experience? Thanks.
 

Ann M.

Well-Known Member
@Ebike Commuter there's a clear explanation on Battery University about why the 85% charge level is normal and good for LiFePO4 batteries and other ebike battery chemistries; in particular a higher per cell voltage shortens the overall lifespan of the cell and in the case of LiCo and LiFePo4 cells, puts them at a higher risk of overheating and thermal run away. Lithium cells do not need to charge to 100% to get best range and lifespan; in fact it's quite the opposite to the care needed for old style SLA batteries.
 

George S.

Well-Known Member
If you are asking what the true capacity of a battery pack is, better not to start with a year old pack. I assume you set the Satiator to 100% charge (it can be set lower) and this is what you get after a full discharge on a bike, with the BMS limiting the discharge.

Could be:
1) normal loss of capacity
2) optimistic ratings of the pack. Even new packs seem to come in down 4-7% with real discharge tests.
3) one weak cell will limit what the pack regulated by the BMS can deliver because the lower voltage will be 'tripped' due to lower voltage in one cell. The BMS has to prevent any cell from over-discharging.

Start where you are, whatever the 'real' capacity is, and see how the packs do, over time.

I always suggest that people get a pack with about double the capacity they need. That gives you room to maneuver.

This is an interesting video and comments about capacity:

 
The Grin Technologies Satiator used to charge the batteries was set to the same Amps and Voltage values as the OEM charger. For the 36V Easy Motion 11.6 Amp*Hour battery, the fully charged voltage was 42V and the charge current was 2 Amps. The Satiator uses the common 2 stage charging scheme to achieve a full charge for a Lithium Ion battery. In other words, it charges at constant current, 2 Amps in this case, until 42V is achieved and it then applies a "saturation charge," by gradually decreasing the current while maintaining the 42V. The maximum voltage, charging amperage and battery type can be set by the user. Charging is complete when the current drops below a pre-programmed low value. If one were to cease charging immediately after the voltage reached 42V, then the battery would be expected to contain only ~85% charge, as described in the Battery University website above by @Ann M. However, that is not the case here, as a saturation charge was applied by the Satiator automatically, ensuring a "full," charge.

The table below shows the cumulative Amp*Hours of charge accepted by the battery at each voltage value. As can be seen from the table, the highest value, 9.7 Amp*Hours, is ~84% of the stated capacity. The battery was ~7 months old at the time of testing. The other Easy Motion battery evaluated yielded nearly the same result, 82%, and was ~3 months old at the time of testing.


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It seems like possible explanations based upon the feedback above are some combination of the following:
1.) Not all of the capacity is usable because of the low voltage cutoff of the BMS, as mentioned by @JoePah
2.) Stated capacity assumes a "full," charge above 42V.
3.) Degradation of battery after 3-7 months of use.
4.) Ideal case/nominal, ratings for battery.
5.) cell to cell variation tripping the low voltage cutoff, as mentioned by @George S.

I'm curious if others have observed the same phenomenon with their battery packs. Per the video above and the Kinaye website, the Sonders and Kinaye batteries delivered 94% and 92% of their stated capacities respectively when discharged from 42V to 32.6-32.7V. This represents a discharge of ~1.6V more than the Easy Motion battery, so could explain some of the lower actual vs stated capacity of the Easy Motion battery. However, the video tests represent the capacity delivered, vs the results in the table above which only show the amount of charge accepted by the battery. During discharge there could be losses due to heat etc., so that the Easy Motion batteries tested could deliver even less than 82-84% of stated capacity.

Regarding the Satiator question from @Jonah it can be used with a wide variety of battery types: Li Ion, Lithium Iron Phosphate, Lead Acid etc. However, it only comes with XLR and Anderson connectors. If your charger port is of a different type, the Satiator will not work out of the box. However, it is fairly easy to cut the wires on an OEM charger and solder male and female XLR connectors to the resultant wires ends of the OEM charger. In this way, either the OEM charger or Satiator can be used.
 
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The Easy Motion bike also comes with a display unit that provides numerical values for %battery charge. The %battery charge does not correlate linearly with the battery voltage, as shown in the chart below. However, it does correlate linearly with the amount of charge accepted by the battery, shown in the other chart. I'm also curious to know if the display values drop over time as the battery deteriorates.


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