life of battery

[jeohearn]

I have an ebikekit 36v 10ah purchased about 2 and 1/2 years ago or so (just before they stopped selling them). It comes with a rack adapter so that it can slide onto my back rack.
After a little over one year of commuting (7 plus amp hours round trip, much less in the summer months; charging both at home and work,) I had 9 out of the 10ahs left. Today, after another full year, I ran it dry again to find out (with a simple watt meter) that I had 8ahs left (I was expecting less, so I was happy).
I am trying to get an idea about how much longer this battery will last me. My main question is: does the battery lose its amp hours exponentially over time? In other words, should I look for less than 7ahs when I test again next year, maybe more like 6?
I will need to have at least 5ah to continue commuting without discharging more than 80% if I account for using up to 4ah each way...and that of course allows for no errand on the way home that will use additional ahs!
Thanks for any ideas.

 

[DAND214]

Did you really have 10ah to begin with?

9 a year later and 8 now. I'd say that's pretty good.

That's probably better than Jason thought you would of got.

You got a good one, they probably would of still be selling them if all were that good.

As for what to expect, who knows.

Dan

 

[cal3thousand]

Thanks for sharing. Keep posting your findings here... we don't have this knowledge unless someone as yourself puts it here. So many people post without followup.

 

[Ypedal]

http://ypedal.com/EBK/ebk.htm

If you got the 10ah prismatic pack as shown above, that one was the first off the production line before ebk imported them, that one has been abuse tested, cold weather tested, lent to a bunch of newbs to do their worst since 2009 .... still in use by a local and i capacity tested it at 1C a few weeks ago at 7.5ah, actual cutout on the 20amp controller gives 6.5ah before the BMS starts to kick out ...

I guesstimate cycles on this pack to be well over 500, will likely be retired next year.

 

[Ykick]

http://ypedal.com/EBK/ebk.htm

If you got the 10ah prismatic pack as shown above, that one was the first off the production line before ebk imported them, that one has been abuse tested, cold weather tested, lent to a bunch of newbs to do their worst since 2009 .... still in use by a local and i capacity tested it at 1C a few weeks ago at 7.5ah, actual cutout on the 20amp controller gives 6.5ah before the BMS starts to kick out ...

I guesstimate cycles on this pack to be well over 500, will likely be retired next year.

I got one of those too and this past Spring 2012 measured 9Ah. Not that many cycles since it's mostly used on a recreational bike and treated gently but it's been charged at least once a month used or not.

Also have one of the 9Ah packs back in CA. It's been powering an old brushed hub bike but still works pretty good although I've never measured it's absolute capacity it delivered 7Ah on many occasions.

Both of these packs near 2-1/2 years old now. I think what kills 'em is if you don't charge every month and the BMS drains cells to 0V.

 

[dnmun]

actually the BMS on the ebikekit.com packs use the O2 micro based BMS and it takes power from the top of the pack, not from the lower 4 cells as the ping packs with the signalab BMS does.

the biggest problem i had with these packs using that BMS is the slow rate of balancing. when a cell reaches the 3.9V HVC then it turns off the charge and waits for the cell to drain down through the shunt resistor all the way back to 3.65V before turning on again.

68 ohm shunt resistor so the shunt current is only 52 mA.

 

[dogman dan]

A lot will depend on which motor you got. Chances are, if you got the little gearmotor you will get at least another year, or more.

But if you have the larger dd motor, at some point it will start to really pound that battery. As your capacity goes down, the c rate of your discharge goes up. At some point it will be at a tipping point that really hammers the cells with a too high c rate.

If you have the 15 amp controller on the little motor though, you'd have to be down to 5 ah before it got really bad.

Winter will be when the battery suffers the most, so maybe a new battery for christmas?

 

[jeohearn]

Thanks to everyone for their input. Yes, to the gentleman who included a link to the battery, it is in fact that same battery pack. Well, if I attempt to digest and integrate all of your input I ought to be happy if I make it to the end of this school year (June 2013) with this pack.
Thanks,
Jeff

 

[jeohearn]

Forgot to mention that I have the Aetoma front hub motor -probably new 3 years ago. It would seem it was their stock motor with a stock controller (36 volts).