Yes, there certainly is a correlation and measuring these is exactly the same thing, and again it's done by the ladder IC system I mentioned.
The reasons the shaver seems to get it virtually right are threefold. First, the small shaver batteries have very little depth of electrolyte, probably also fairly low particle density, so the voltage release of the electrolyte surface at the electrodes fairly accurately reflects the whole charge density. by contrast, our bike batteries have considerable depth of electrolyte which is of very small particle and very high density consistency to hold the very large charge. The surface voltage release therefore doesn't accurately indicate the charge density elswwhere in the electrolyte, it takes time for the current to work it's way out, hence the chemical exhaustion that's mentioned elsewhere.
Secondly, the shaver batteries are being virtually fully discharged each time, and this resets the ladder IC circuit base point, giving better measurement accuracy. When we part charge Li-ions to maximise their life, the base point accuracy is progressively lost, we need to discharge fully from time to time to maintain it.
Thirdly, there are typically just two cells in the shaver, both of very predictable performance due to their small size, so the estimation of capacity held by means of measurement of tiny voltage variation is quite accurate. There are 10 cells in our Li-ion batteries, of not so predictable performance, and the voltage variation of the individual cells is not consistent, so the guestimation from the sum of those isn't going to be very good. Matters are just as bad with NiMh, for although they are more predictable in performance, there's the variations of 30 cells to deal with.
The point to remember remains the same as I keep saying on this subject, we cannot measure the actual amount of charge in the battery by electrical means, it's a chemical device. All we can do is measure the voltage release at the electrode/electrolyte interface and make a deduction from that, which may or may not be accurate. Also, since opening the throttle causes a voltage dip as the motor takes up current, the accuracy will always be haywire as we ride.
The reasons the shaver seems to get it virtually right are threefold. First, the small shaver batteries have very little depth of electrolyte, probably also fairly low particle density, so the voltage release of the electrolyte surface at the electrodes fairly accurately reflects the whole charge density. by contrast, our bike batteries have considerable depth of electrolyte which is of very small particle and very high density consistency to hold the very large charge. The surface voltage release therefore doesn't accurately indicate the charge density elswwhere in the electrolyte, it takes time for the current to work it's way out, hence the chemical exhaustion that's mentioned elsewhere.
Secondly, the shaver batteries are being virtually fully discharged each time, and this resets the ladder IC circuit base point, giving better measurement accuracy. When we part charge Li-ions to maximise their life, the base point accuracy is progressively lost, we need to discharge fully from time to time to maintain it.
Thirdly, there are typically just two cells in the shaver, both of very predictable performance due to their small size, so the estimation of capacity held by means of measurement of tiny voltage variation is quite accurate. There are 10 cells in our Li-ion batteries, of not so predictable performance, and the voltage variation of the individual cells is not consistent, so the guestimation from the sum of those isn't going to be very good. Matters are just as bad with NiMh, for although they are more predictable in performance, there's the variations of 30 cells to deal with.
The point to remember remains the same as I keep saying on this subject, we cannot measure the actual amount of charge in the battery by electrical means, it's a chemical device. All we can do is measure the voltage release at the electrode/electrolyte interface and make a deduction from that, which may or may not be accurate. Also, since opening the throttle causes a voltage dip as the motor takes up current, the accuracy will always be haywire as we ride.
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