Question for the lipo gurus

[Philistine]

This is a question for the lipo gurus. My question is this, if you took two lipo batteries, and you discharged one to 50% of its rated AH used, then recharged, and did this 100 times. And you took another battery, and discharged it to 25% of rated AH used, and recharged, and did this 200 times, would there be a noticable difference in the lifespan/health of the two batteries, and if so which is better, and how much difference would there be? (if the 100/200 is too short a span to see a difference then insert whatever would be a substantive period)

The basis of my question is, that on my Yuba I have a 40AH pack, and although sometimes I use the available extent of the pack when I do big cross city rides without charging, most of the time I can choose when I recharge, and because I like having the highest voltage possible, I tend to recharge as often as is practicable. I was wondering if repeated short depth charging drastically shortens battery life (ie, if I am constantly recharging with only 25% of battery used, is that shortening the life span much compared to recharging less, but going deeper. One reason I also like charging frequently (ie as soon as is practical to recharge) is that it also keeps the cells more balanced (going as shallow as possible). But it got me thinking about lifespan.

What is the thoughts of the gurus?

I doubt the answer will change my behaviour, as in the year and a half I have been running my packs I have seen very little performance loss (other than packs I have blown up or damaged myself), but I was interested from a theoretical perspective as well, ie what is it that wears down a battery, AH extracted from a pack over time, or the rate of charging?

 

[chilledoutuk]

Its generally accepted that the biggest impact on cell life is DOD depth of discharge which means charging whenever you can as long as your cells arnt roasting will prolong the life of your pack.

Also keeping the charge rate down as low as you can will be more gentle on the cells.

For example if you need to put back about 8ah into your pack and you plugged your pack in whilst you work or whatever divide that figure 8ah by the time in hours you have to charge your pack and then go up a little more to allow for the cccv period of the charger.

 

[dogman dan]

I would tend to say that both regimens would tend to result in a good lifespan. Both use a very light dod.

Only a real world test is going to show the truth.

I think we can say that charging you battery at every opportunity cannot harm it, provided you are not charging improperly. So good to keep charging it, if you don't overcharge, or charge at too many amps.

Charging to 4.1v is said to have a very beneficial effect, so doing that when you don't need all of it makes a ton of sense.

 

[SamTexas]

My question is this, if you took two lipo batteries, and you discharged one to 50% of its rated AH used, then recharged, and did this 100 times. And you took another battery, and discharged it to 25% of rated AH used, and recharged, and did this 200 times, would there be a noticable difference in the lifespan/health of the two batteries, and if so which is better, and how much difference would there be? (if the 100/200 is too short a span to see a difference then insert whatever would be a substantive period)

I would like to know too.

I think we've all heard of the following recommendations:
1) Keep the voltage ceiling to around 4.10V.
2) Keep the voltage floor to around 3.50V.
3) Charge and discharge at a slower rate than specified by the manufacturers.

They sounds reasonable. But do they really help? If so, by how much? I have yet to see hard data and would love to get my hands on them. This kind of test is definitely beyond an individual's ability and resources.

 

[neptronix]

I believe YKick is on 600 cycles and counting.. running a quite low DOD.

chopping voltage off the top seems to extend the battery life of most non-lifepo4 chemistries.

 

[chilledoutuk]

I believe YKick is on 600 cycles and counting.. running a quite low DOD.

chopping voltage off the top seems to extend the battery life of most non-lifepo4 chemistries.

indeed i remember reading a release from a123 when they released there cells about the reason for them being able be stored and not loose hardly any charge when kept full was because they were much further from the breakdown voltage of the chemistry than standard lipo tech.

i have also read that storing your lipos at reduced temeratures helps the shelf life in lipo tech.

I like to have my packs ready to go so i would prefer to store them charged but chuck them in the fridge to protect them a bit better from the reduced shelf life of storing packs with full charge.