What's Better? Use up more Ah's or Charge more often?

[Ottodog]

I have a question about my Battery. It takes me 3.5 Ah to get to work and back. Three trips would be 10.5 Amp Hour out of 13.5. which is right under 80%. If I go twice it would only use about 7 Amp Hours out of 13.5 but would require charging it more often.

My question is, what’s better for the Battery? Charge it more often after using 7 Amp Hours, or Charge less often but use up more of the capacity at 10.5 Amp Hours?

 

[Lurkin]

Pros of smaller battery
- lighter
- smaller
- quick to charge in full
- cheap

Pros of larger battery
- more capacity. As capacity decreases with use, a larger battery is more likely to remain useful even with reduced capacity
- more range. Can use it to do unanticipated trips.
- more likely to be useful if your power requirements increase

I went for the larger option.

Note: can always get smaller batteries of the same voltage etc and put them in parallel...

 

[Ottodog]

I actually already have the battery and it's 13.5 Ah. I'm just wondering what is the best way to prolong it's life. Use less of it's capacity with more charging cycles or use more of it's capacity with less charging cycles. There seems to be some debate about which is healthier for the battery.

 

[prensel]

I would say charge more often.
You get more cycles out of lithium by not depleting it completely.
Hence Tesla and alike prevent over and under charging of their li-ion cells.

 

[Sunder]

It's hard to see on a log scale above, but you get more total stored energy when you have multiple small discharges than fewer large ones. That is, you might 2,000 x 80% cycles, or 4,500 x 40% cycles. and 10,000 x 20% cycles.

So yes, the advice is to charge at every opportunity - but always right before you use it, as storage above 80% SOC shortens the shelf life of the battery.

 

[dogman dan]

Leaving 3 ah on the table is already pretty good. I would not sweat discharging to around 75% discharged. I see no harm really, in that. Sure, it should be better to charge every time, but at some point we have to decide if the effort is worth it. What I mean is, if the recharge is easy and at home, why not. But if it means carrying a charger around, charge when you get home.

So the real question is, if you charged every trip, would the battery spend lots of time fully charged? This doesn't harm the battery per se, but it does wear the battery a little bit faster if it sits around fully charged, and in a warm place for weeks at a time. To lessen that can be good, so when the weather is warm, it could make sense to run three trips then charge.

In this case, it almost becomes flip a coin. Gain some charging every trip, but maybe lose it back if the battery would not be discharged again immediately. But if its always an easy charge, and you can ride right away, go ahead and charge every cycle.

Bear in mind, some of this reluctance to charge often comes from bad experiences with NiCad or cell phone chargers that sucked. I once had a phone that ate a battery every six months. As I learned about batteries, I found the cell that should have been charged to 4.2v max, was getting charged to 5v every cycle. no surprise I'd learned to charge that phone as seldom as possible. But your charger should be ok, and safe to use often.

Sorry if that answer is a bit non committal, but the fact is either way you decide to go is OK enough. Do what is convenient for you. I'd be inclined to take the long way home if my ride was that short, for the fun of the ride. So I'd want to have at least half a charge when I left work.

 

[Ykick]

It can be quite a conundrum, eh?

For modest range most folks will prefer lightweight bike so as long as you’re not hammering the cells a small capacity pack can make a lot of sense for the majority of riding.

Those occasions you need more range? I just carry a reserve in a backpack and/or parallel more capacity in whatever format best fits the bike.

It's no secret draining batteries at the lower end of their SOC (state of charge) increases internal temperatures more than draining at higher SOC. How much do those higher internal temperatures influence lifespan is really anybody’s guess? But for that reason, I will never hesitate to top-off a battery pack given an AC outlet opportunity and lightweight, durable, easy to carry charger.

 

[MrDude_1]

Build the biggest battery you can fit/afford.

If you do that, you never discharge it very much... so dendrites are less likely to form... and when you do charge it, dont fully charge it, leave a bit of headroom.

doing this, you may only have 80% of the capacity available, but:

1. The battery will last MUCH longer. Note every EV with a warranty or reputation does this.
2. You can charge faster. The battery is larger, so the 1C rate is higher.
3. You have more amperage available.. so when you do ride, it has more "punch"
4. The occasional extra long ride is possible.. you're not just limited to commuting.


downsides?
First is cost. You're paying for extra batteries or higher capacity ones.
Weight. The vehicle weighs more.
Charger costs... If you want that quick charge advantage, you need to pump more amps into it. If you're not building your own charger, it costs more.

 

[2old]

Since it's been reported that Tesla is able to guarantee their batteries for eight or whatever years by not allowing them to neither charge past 80% nor discharge lower than 20%, it seems moot (TO ME, a relative newbie). I have the luxury of charging my battery from "mid charge" to 100% just before I use it, so that's the protocol. Another possible solution is to use the Satiator or Luna Cycles $100 charger (which allows the battery to be charged to 80%, 90% or 100% with the flick of a switch).

 

[999zip999]

Always best to have charged battery, but two trips 7ah is a great idea before charging.

 

[Overclocker]

I actually already have the battery and it's 13.5 Ah. I'm just wondering what is the best way to prolong it's life. Use less of it's capacity with more charging cycles or use more of it's capacity with less charging cycles. There seems to be some debate about which is healthier for the battery.

3.5ah out of 13.5. that about 25%

charge the pack to 75%. use it down to 50%. repeat

keep it cool

your pack will probably last longer than you need it to if you do this

 

[Lurkin]

Probably also need to consider the time it takes to charge. A smaller battery will charge in full and balance, larger maybe not... hence mine gets charged in full and balanced after the morning commute, but does not get a complete charge at night (only have it charging while I am awake, which is about 1 - 2 hours after getting home from work).

 

[Sunder]

Since it's been reported that Tesla is able to guarantee their batteries for eight or whatever years by not allowing them to neither charge past 80% nor discharge lower than 20%, it seems moot (TO ME, a relative newbie).

If I were an electric car engineer, I'd be doing that for the first year or two, then releasing 2 percent extra capacity every year. (I.e. in year 2, charge to 81%, discharge to 19%, year 3, charge to 82%, discharge to 18%) That 2% can compensate for the loss of range from an aging battery, giving an illusion that the battery hasn't degraded at all.

Maybe I should go work for VW....

 

[liveforphysics]

If your goal is maximum cell life, charge to 85% of maximum capacity, and recharge to that 85% as often as possible (so most shallow cycles). Many cells will last many 10s of thousands of shallow cycles like 85% SOC to say 40% SOC.

If you have a ride when you need the full pack capacity, charge to 100%.

 

[Ottodog]

Thanks everyone for all the replies. It seems clear that using less of the total capacity and charging more often is the way to go. I'll take her twice (use 7 Ah) and then charge it after every second use That's certainly doable. I appreciate the advice. These batteries aren't cheap and I'd like it to last as long as possible.

 

[Ottodog]

If your goal is maximum cell life, charge to 85% of maximum capacity, and recharge to that 85% as often as possible (so most shallow cycles). Many cells will last many 10s of thousands of shallow cycles like 85% SOC to say 40% SOC.

If you have a ride when you need the full pack capacity, charge to 100%.

I'm intrigued. How do you stop the charger at 85%? Doesn't the charger have to balance the pack after the charge cycle? How would it do that if you stop the charger early? I'm not questioning, I just don't know. Do you just kind of keep an eye on it and stop it at a certain Voltage?


ETA: My Charger is set to charge this pack to 96.6V

 

[Lurkin]

If your using a prebuilt pack with BMS and basic lithium charger, you can't really or not easily anyway. It will balance when the BMS has been programmed to.

 

[Ottodog]

If your using a prebuilt pack with BMS and basic lithium charger, you can't really or not easily anyway. It will balance when the BMS has been programmed to.

Yep. It's a Prebuilt. Came with a BMS, and it's own Charger. They told me it would balance the pack at the end of the charging cycle.

 

[Lurkin]

Contact who you bought it off to find out if the BMS is programmable or open it up to find out what it is, then whether you can reprogram it. The first of these options is better, because opening it up is likely to void your warranty.

 

[dogman dan]

Second charger that only charges to 85% would be the easy way to do the 85% to 60% routine. Then occasionally, charge to 100% with the other charger and ride immediately, to get balanced once in a while.

I hesitated to suggest undercharging at first, mostly because of the cost of the new charger, and the slight inconvenience. At some point, we have to decide what is first priority, maximum battery life, or maximum convenience. Given the very short ride you do, it's very likely that your battery will time out in 3-4 years, rather than get used up. This will be the result of using the battery in the real world, unlikely that in summer it will be ridden in a cool environment, or have shade covered parking all day while you work. Because of this, I'm inclined to say the thing to do is just charge every 2nd or third ride, and not worry too much about undercharging all the time.

But if you find yourself needing a new charger anyway, EM3ev has one with a switch so you can choose a 90% charge anytime. I use one often, and typically don't need 100%, so I charge to 90% a lot. Why not, if it's that easy. But I still expect that battery to start really losing capacity this summer, it's 3rd summer.

 

[Ykick]

Luke’s correct but any “practical” (chose that word carefully) difference of battery pack lifespan you may realize from 85% top charging is gonna be very hard to notice and or measure in the day-to-day world of riding/using, IMO.

Especially, if you “guess wrong” a couple times and wind up over discharging the battery pack or merely discharging it at lower SOC because it didn’t have enough charge starting out to get you where you estimated you need to go.

Apart from over-discharge, one the most “practical” damaging things we can do to our Lithium chemistry is leaving them sit fully charged for days, weeks, months on end.

With this in mind, I charge to 70-85% SOC immediately following use and stop there. But then, will top it off to 100% a few minutes/moments before riding.

Best of both worlds, IMO. You won’t inflict as much chemical damage from sitting fully charged for long periods of time coupled with less risk of deeply discharging and excessively heating cells delivering current at lower SOC.

For the grossly “unapproved” stuff I know some of us have experimented using 110% or more SOC applied immediately before use in order to maximize range. In my case, those cells abused in that manner still work fine to this day, many years and cycles later.

Remember, “practical” difference(s)…

 

[MrDude_1]

Luke’s correct but any “practical” (chose that word carefully) difference of battery pack lifespan you may realize from 85% top charging is gonna be very hard to notice and or measure in the day-to-day world of riding/using, IMO.

I disagree. Look at any modern smartphone. When you top them up constantly, in about a year to year and a half, you can see a noticeable reduction. Lipo capacity loss is real.

Especially, if you “guess wrong” a couple times and wind up over discharging the battery pack or merely discharging it at lower SOC because it didn’t have enough charge starting out to get you where you estimated you need to go.

There should be no guessing... your bike should cut out before it over-discharges anything.

 

[Ykick]

Topping off to 100% and immediately consuming top charge is significantly different than sitting 100% SOC (which majority of cellphones do) for long periods of time.

BMS should protect from extreme ODDV but that doesn’t exclude higher average cell temperatures when regularly discharged @ lower SOC.

My point is mostly about being “practical” for riding purposes - pick your poison…

 

[wineboyrider]

I have 2 chargers for my 12s lipo pack. On the 2.5 ah charger I use to charge to 85% and set the voltage at 48.5 the other charger a 10amp meanwell charger I have set to 98% or 50v . I rarely charge to 100% as the meanwell charger can charge my 12ah pack in about an hour and half from empty, but my pack is rarely discharged more than 50%.

 

[MrDude_1]

Topping off to 100% and immediately consuming top charge is significantly different than sitting 100% SOC (which majority of cellphones do) for long periods of time.

BMS should protect from extreme ODDV but that doesn’t exclude higher average cell temperatures when regularly discharged @ lower SOC.

My point is mostly about being “practical” for riding purposes - pick your poison…

but if your make your lipo top charge 4.15 or less instead of trying to pack in 4.2 (with almost no gain anyway) you get a bike thats ready all the time, AND it doesnt kill the battery.

I just like the whole plug it in when I get home/work/shopping and forget about it.... no worries. People stress about charging too much... just make sure you can do it at or near a 1c rate... you dont HAVE to keep it that high, but If you do, it lets you be "empty" to "pretty much ready" in 40mins... then it tapers off....