When is the battery dead?

It is a good thing that even at my age I have no problem asking silly questions, but when is the battery dead?

A nice ride of 13.1 miles today used just over five AH and it seems like 246 WH, the batteries still read 49.6 volts when I turned everything off. The entire trip was done at slow speeds of 13 to 18 MPH and included one good sized bridge. (that's a hill to non flat landers)

I've read comments that 48 volts is dead. I would believe that except that I've run below that several times, to 46 volts that I remember.

I've also read that 80% of full charge is dead. For me, 80% of 52 volts is 41.6 volts and I've never even come close to that If I misunderstood and it was 80% of total WH then it would be 460.8 WH which means I could only use 115 WH and I use more than that regularly.

Today, since I went slow ALL of the time I don't recall ever seeing more than 24 peak amps and that was when I was going up the bridge the second time but naturally as soon as the downhill part starts the number drops to .0 something. I tried to keep my cruising speed averaging 3 - 4 amps which I could do when there was no headwind. Headwinds would knock it up a couple of amps.

The little yellow low power light on the throttle never came on which it does when the batteries get tired, it probably would have had I tried to gain any serious speed on the last mile or so.

So, the question is, since I don't think I was in any danger of having to pedal if I went three or four more miles, when would my batteries have died. (It took 90 minutes of charge for the green light to come on the charger)

Mike

Depends on mainly on the battery chemistry. What kind of batteries are these?

Pack capacity versus pack voltage also depends on how well the individual cells in the pack are balanced, their calendar age, their discharge cycle age, and the ambient temperature.

12 volt SLA's are comprised of 6, 2 volt cells -- any internal imbalance another source of variance.

It depends on how long you want your pack to last. Greater DoD (Depth of Discharge) reduces pack longevity.

It also depends on chemistry. If SLA, if your pack is nominally 48V, 48V while running could be a good place to stop, if you want to keep your packs decent for a couple of years.

http://www.batteryuniversity.com/partone-13.htm

B&B 4 each 12 volt 12 AH

Mike

Again, it depends on many factors, but TD is generally correct, 2.0 open-circuit volts per cell (48.0v for a 48 volt pack) is 70-80% depleted for SLA, and a good place to stop, else cycle life takes a major hit.

For other chemistries, 70-80% depth-of-discharge, good stopping point is:

NiMH/Nicad: 1.0 open-circuit volts/cell (40.0 volts for a 48 volt pack)

Li-ion/Lipo/LiMn: 3.70 open-circuit volts/cell (37.0 volts for a 10-cell 37 volt pack).

LiFePO4: very flat discharge voltage so hard to correlate with capacity, but less than 10% left at 3.0 open-circuit volts/cell. Probably a good stopping place for LiFePO4, which seems to tolerate deep discharge much better than other chemistries.