Tonight's run was to test my oldest battery. I did that by running it until it was depleted. The battery ran out of juice after using 715 Wh. When the battery was new it had 800+ Wh of usable power. This represents about a 10% loss. Not bad considering the battery is almost 5 years old.
The battery was originally rated for 16 Ah but tonight it only delivered 14.8 Ah. This reduction in Ah is consistent with the reduction in Wh.
Data for tonight is incomplete because of the test.
Start time 8:45 pm
Temp 13.1 C
Start Voltage 58.0
Finish Voltage 40.1
Ah 14.8
Trip Distance ? km
Distance 10731 km
Time n/a
Av. Speed 27.7
Trip Wh/km 19.6
Trip Wh 715.0
UPDATE:
I also measured the number of Wh used per Ah.
So the fully charged battery has 15 Ah it also has 715 Wh of usable energy.
Using the above numbers one would expect the battery to deplete at the rate of 48 Wh per Ah. But this expectation would be wrong.
This is because the battery voltage is also going down as it depletes.
Starting voltage with no load is about 58 volts and final voltage with no load is about 43 volts - a drop 15 volts.
Remember: volts x amps equals watts (or volt/amps).
So
1st amp x 58 volts = 58 volt/amps
2nd amp x 57 volts = 57 volt/amps
3rd amp x 56 volts = 56 volt/ams
14th amp x 44 volts = 44 volt/amps
15th amp x 43 volts = 43 volt/amps.
(NOTE: it is just coincidental that the total voltage drop and the number of Ah have the same number)
You can see that the 1st two Ah have (58 + 57)115 volt/amps or Wh of usable energy while the last two Ah would have (44+43) 87 Wh of usable energy.
Conclusion: when you only partially charge your battery the missing Ah have the highest Wh per Ah. So a 90% charge does not mean that you actually have 90% of your energy potential.
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