Phil Fouracre wrote:Just seen this reply - can I ask a couple of questions that have been interesting me as a keen ebiker! how long is defined as ‘not in use’ re batteries, and is there a practical/accurate way to check charge % level?
I tend to class as not in use more then a couple of days, a fully charged battery lessens the life span as it will cause cells to age early by loss of capacity. Left fully charged the ions interact and small nano particles are deposited on cell Anode/Cathodes, the deposits cause voltage flow to suffer and in turn cause cells to heat up (internal resistance). IR is a major cause of voltage sag .
In the short term damage is minimal but longer term 2- 3 weeks or months on end the aging will hasten.
A battery down on capacity will still be useable for several years but range is somewhat affected and voltage sag becomes more prevalent ( another sign of aging ), where as a battery looked after a bit more carefully will keep it's capacity and voltage drop will be more linear. Voltage sag is a sign of higher internal resistance though all battery's suffer sag as this is normal when a load is applied, an aged battery with higher IR will suffer more so and will cut out if too high a load is asked of it. When a higher load is applied voltage will readily collapse then bounce back as if all is ok.
Ideally charging to only 4.1v would be better as the top 10% of the voltage holds very little mah/capacity and is often depleted very quickly with in the first couple km's of use. However all generically used BMS are set for 4.2v for balance charging, trying to only charge to 4.1v or less with one fitted cause more issues then it solves so it's not worth the bother. Instead it is better to manage the battery charging so that you only charge approx. 6 - 12hrs before use.
If I go out on a long ride on return I only charge partly if the voltage is below 3.6v per cell/group and stop the charge at between 3.75 - 3.85v, I then leave the battery and fully charge up several hours before I need it again.
You can buy for £'s a simple battery voltage gauge that will give three readings, a battery segment bar, voltage readout and a % readout. A battery's bms has bottom end voltage cut off (known as LVC), this is normally 3.2v (0 -10%) per cell /group. The top end we know is 4.2v (100%) per cell/group, although not 100% linear you can allow 10% for each 0.1v decrease.https://www.ebay.co.uk/itm/12V-24V-36V- ... 516d1dccb4
Half the price on Aliexpress, I always add one to my batteries that I build.