At what capacity loss would you consider replacing batteries

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Offroader   10 MW

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At what capacity loss would you consider replacing batteries

Post by Offroader » Apr 11 2015 10:05pm

I'm just trying to get some peoples opinions here when they will consider replacing their batteries because of capacity loss.

Lets assume the batteries internal resistance is fine and there is no problem with the batteries other then capacity loss from usage cycles and age.

At what percent capacity loss will you consider replacing them?

My batteries are coming up on 3 years old and the capacity from 4.1 to 3.7 went from ~3400MAH to ~2700MAH per pack. Almost 20% loss. I assume the batteries will work fine but keep losing a certain percentage of capacity every year. So I have to make a decision at a certain point when it makes sense to replace them.

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lester12483   10 kW

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Re: At what capacity loss would you consider replacing batte

Post by lester12483 » Apr 11 2015 10:45pm

If the capacity gets you where you need to go then keep them for now. You can always buy a newer battery and use the older battery as a backup.
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Lebowski   1 GW

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Re: At what capacity loss would you consider replacing batte

Post by Lebowski » Apr 12 2015 2:12am

I would only replace when the capacity is so low it's no longer sufficient for my commute... I have 400Wh and a 6km commute, so they will last really long :mrgreen:

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Re: At what capacity loss would you consider replacing batte

Post by Punx0r » Apr 12 2015 4:17am

Or the internal resistance becomes so high the voltage sag is intolerable.

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dogman dan   100 GW

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Re: At what capacity loss would you consider replacing batte

Post by dogman dan » Apr 12 2015 6:41am

Bingo. I have run packs to the point of 50% capacity. But by then they have so much resistance, they can't pull much load anymore. So I pile them up into a huge pack, like 20 ah, and then can pull 300w from it ok. If I pull enough watts to make it sag more than a volt, then the capacity plummets. On the recharge, it will take forever to fill as well. Charger churning away, doing nothing much but gently warming the pack. :roll:

But I have still used them, to extend my range some when I desperately need that additional 15 miles of range.

The other thing I do is run nearly dead packs on my 24v mower. Again with the big capacity, paralleling a pile of them. Then with the motor pulling hard on them, not much work out of them, but it gets the lawn mowed another season for free. I might not get the lawn mowed all in one go, but nothing wrong with pushing the motor 10 min a day for 3 days.

But if they are starting to stink, chuck em. Or if they realllly puff.

At 3 years, you have gotten the life you'd expect from them. So getting some more is not a bad idea. Certain sizes may become hard to get soon, as summer comes and the drones fly. So if they have what you like now, not a bad idea to nab em now.

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Re: At what capacity loss would you consider replacing batte

Post by LockH » Apr 12 2015 7:26am

Welcome to the World of Electric Traction! (Where use becomes an exercise in NOT using (minimizing) battery use!) Hehe (sorry) Back in the daze of lead-acid, old/worn out batts made great door stops (before taking them somewhere for recycling). Good point re backup/secondary uses though. Used to ride regular routes where "not enough range"/too much pedaling (kicking a standup scooter) got to be "too much exercise". Learned to love gravity (any down hills). Up hills, not so much. Even windy days good/bad (just sometimes sitting down on the foot deck/lessening "aero drag" made for dramatic improvements). Dunno how linear your capacity losses are over time, but at some point it used to "cliff dive". So loss of any sort was a sort of a "warning sign". And PBA batts (twox 12V 10Ah in series) were so "cheap" to buy was buying "extra" just to have spares on hand. With next pack, consider having a "spare change" bucket or something for saving bills for the "next time"/repurchase. Like "going to the gas station" (but horribly expensive, and waaay less stinky)... occasionally. Sorta like the old "nickel in a cuss box".
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amberwolf   100 GW

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Re: At what capacity loss would you consider replacing batte

Post by amberwolf » Apr 12 2015 9:26pm

When your batteries turn into internal combustion devices it's definitely time to replace them. :P

But I'd agree that when A) they no longer have enough capacity to do the ride or commute with some extra margin for wind/detours/etc, and B) when the sag is intolerable and/or they simply can't produce the current needed, it's time for replacement, or adding a new pack in parallel.

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Re: At what capacity loss would you consider replacing batte

Post by mvly » Apr 13 2015 2:39am

I have hobbyking nanotech lipo and it is roughly 50%-60% now. It has been more than 3 years and it still go on chucking. Since it is lipo the internal resistance is still in check. It does sag a bit compared to when it is new but recovers fine and still provide at least 50% easy assuming you fully charge it and use it within a week. Self discharge is a bit higher i noticed.

I might retire it soon, but it is still cranking so i dont know what i will do. I got about 6K miles on it i think. It was expensive compared to today standards, but hey when i got it it was the only real option at the time.

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dogman dan   100 GW

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Re: At what capacity loss would you consider replacing batte

Post by dogman dan » Apr 13 2015 7:56am

Tired old batts that started with a great c rate would likely do a lot better when old, than ones labeled 20c that likely were never much better than 10c in reality. If the sag is still tolerable, then they are still usable.

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Ykick   100 GW

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Re: At what capacity loss would you consider replacing batte

Post by Ykick » Apr 13 2015 8:58am

Yep, when sag is too bad it's time. But, I've also had old RC Lipo which sagged too much in cold winter weather yet came back around enough for one more summer when the temps no longer drop much below 70F.

I'm sure some of us who've rolled on RC Lipo through Winter have already noticed slightly less sag with the uptick of seasonal temperatures.
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Re: At what capacity loss would you consider replacing batte

Post by MrDude_1 » Apr 13 2015 9:50am

When they stop meeting my requirements for capacity or sag.
of course, if you oversize your battery enough, dont fully charge it, and dont fully discharge it.... it will last a very long time.
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