Another battery question-please can you help?

mountainsport

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Feb 6, 2012
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Good day all,

Please stop me in my track here if I am wrong, some if not all sealed lead acid batteries do not have a battery management system (active) or a battery monitoring system (passive), but Lithium-ion batteries do.

For a known fact it is good practice whenever riding an ebike using a SLA battery, you should always put it on charge straight away after your commute, whether the journey was long or short because leaving them sitting uncharged is not very good for the battery cells.

Kindly, i would like to know if this also applies to the Lithium-ion batteries, being that they are fitted with a BMS? Will it harm the battery or cells if left for a couple of days sat uncharged bearing in mind that it had been fully drained and shut down via the BMS for safety reasons. Hope I've explained myself semi ok.

MS.
 
D

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Lead batteries self discharge quite rapidly. If thet go down to 0v, the plates start sulphating, which knackers them. The longer you leave them, the more knackered they become. The controller has a low voltage control, so it will switch off when the batteries get to a certain voltage, but then the batteries go down by themselves thereafter, which is what causes the problem. You don't need a BMS for lead batteries because they tend to self-balance because the individual cells share the electrolyte.

Lithium batteries have very totally individual cells, so they have to be balanced, which is why they need a BMS. Without one, if the cells went out of balance, the high ones could be charged too high, which can cause a fire. They generally have low self-discharge, so they can be left a very long time if charged; however, you can get worn or dodgy cells that self-discharge a bit, which in normal circumstances is still not a problem. The discharge rate of lithium cells is not even. Most of their charge capacity is above 3v per cell, which is where the BMS shuts them off, once get to that level, it only takes a little self-discharge to make a big difference in the cell voltage, so they go down much more rapidly than when they're charged. Most BMSs won't switch on the charging if they go too low, which is when people think that their battery has died, but they can still be revived provided they haven't gone right down to zero. The lower they go, the more chance that their capacity is compromised.

Whichever type of battery you have, it makes sense not to run it right down because that puts it in the danger zone. Once left in the danger zone, the battery will kill itself eventually, so definitely don't leave it there.
 

mountainsport

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Good morning d8veh, thank you for spending time out in explaining how it really works, but is it the BMSs job in preventing this from getting in to this danger zone? If that is the case why worry about the battery being fully drained? Silly question, but how many times can you get away with this before you actually destroy the battery? I can imagine after five or more times you have had it.

MS
 

Alan Quay

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Dec 4, 2012
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Most controllers have a low voltage cut out, so that would protect the battery from being discharged fully while in use. On the SLA systems I've seen, this is all that is used.

The self discharge rates of SLA mean that you should top them up every now and then if not used - when I was using SLA's I had an automated timer that would give them a 1hr charge once a week, just to be sure.
 
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How much lead batteries get destroyed depends on how low they go and how long for, each time yu go too low, the effect is cumulative.

For Lithium batteries, it's a bit different. The BMS keeps them in the safe zone during normal use. It's only when the BMS cuts off the battery when flat, and you leave it there that you get problems, so you're right, you can just leave the BMS to do its job and everything will be hunky dory, but woe betide anybody that runs their battery down and forgets to charge it.

I don't know exact figures, but to put it in perspective: A 10aH 36v battery has about 400wH of charge between 42v and 31v. If it were self-discharging 1 wH per day, you could leave it for a year and it still wouldn't reach it's bottom level of 31v; however, between 31v and 25v, there might only be 10wH of charge, so if you left it for 10 days after the BMS shut it off, there'd be no way back without dismantling and special charging procedures. At that point, most people would be calling their battery dead.

There's also another problem: Once you get down to 31v, it takes very little discharge to take the cells down, so anything that affects balance between the cells has a magnified effect, so you can get balance problems too, which effect range. Some BMSs don't seem to be very good at re-balancing.

I still think that the best advise is to always charge your bike after you use it regardless of how far you've been, except if you've only done a short journey.
 
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flecc

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Oct 25, 2006
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As Mike says, it's more normally the controller that has the low voltage cut-off. The BMS is usually only concerned with charging so has the high voltage cut-off.

As for worrying about a battery being fully drained, the low voltage cut-off is set at a safe level that doesn't destroy the cells. Many users empty their battery almost to that low level on their daily commute but their batteries can still last for as much as two or even more years. Avoiding that minimum safe charge level makes a battery last bit longer, but the whole usable content can be used without very quick failure.

The important thing is to recharge after any emptying, not leaving the discharged battery idle.

N.B. Crossed with d8veh's post.
 

mountainsport

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Feb 6, 2012
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As Mike says, it's more normally the controller that has the low voltage cut-off. The BMS is usually only concerned with charging so has the high voltage cut-off.

As for worrying about a battery being fully drained, the low voltage cut-off is set at a safe level that doesn't destroy the cells. Many users empty their battery almost to that low level on their daily commute but their batteries can still last for as much as two or even more years. Avoiding that minimum safe charge level makes a battery last bit longer, but the whole usable content can be used without very quick failure.

The important thing is to recharge after any emptying, not leaving the discharged battery idle.

N.B. Crossed with d8veh's post.
Although your post was crossed with d8veh's you both had hit the nail on the 'ion' head.

Points now understood :

1. Regardless of battery type charge straight away after every use.
2. Some BMS's do not balance cells.
3. BMS's are mainly used for the protection of the over charging of individual cells.
4. It is the controller that shuts down the battery when there is a recognised low voltage.
5. If a drained battery gets below the minimum safe level cut off point some BMS's can not rectify some cells back to normal.
6. A good BMS and a good battery charger are the most important and vital parts to enhance the batteries performance.
7. Not often, but once in a while it is ok to drain your battery flat to a minimum.
8. What will I do without people on here? Maybe go back to steam driven engine bikes.
9. I love you all, sorry for being a drip.

MS. Thanks for all your support.
 
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I think that you've summarised it very well, which would be useful for others.

There's one thing to add to complete the picture. Some batteries (mainly expensive ones) have a built in fuel gauge, not to be confused with the LEDs that light up when you press a button, but they look similar. For these, you have to run the battery right down to set the fuel gauge and to re-set it occasionally.
 

mountainsport

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Feb 6, 2012
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I think that you've summarised it very well, which would be useful for others.

There's one thing to add to complete the picture. Some batteries (mainly expensive ones) have a built in fuel gauge, not to be confused with the LEDs that light up when you press a button, but they look similar. For these, you have to run the battery right down to set the fuel gauge and to re-set it occasionally.
Do you mean manually? Come on you are confusing the whole understanding process now. Which batteries are you referring to, Lipo's, Lithium ,Panasonic ,not SLA, etc I can recall some time ago this topic had came up about resetting the fuel gauge on the battery.
Now d8veh, you have opened up a can of worms what do you EXACTLY mean by an expensive battery? Please choose your words carefully:p
Some makers may come down hard on you d8veh like a ton of cells.

MS.
 
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Luckily, you and I don't have to worry about this procedure because we can't afford the luxury of batteries with fuel gauges in.
 

flecc

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Oct 25, 2006
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Do you mean manually? Come on you are confusing the whole understanding process now. Which batteries are you referring to, Lipo's, Lithium ,Panasonic ,not SLA, etc I can recall some time ago this topic had came up about resetting the fuel gauge on the battery.
Now d8veh, you have opened up a can of worms what do you EXACTLY mean by an expensive battery? Please choose your words carefully:p
Some makers may come down hard on you d8veh like a ton of cells.

MS.

The "smart" LED meter ones we are most likely to come across are the Panasonic ones for their own crank drive units, and the Kalkhoff-BMZ alternatives for those units. They need to be fully charged on new receipt and then run to as low as possible on the bike. That emptying action sets the zero point so that the meter LEDs reflect the true content thereafter. Over time that zero point can drift out as d8veh has mentioned, so running the battery very low from a full charge can then reset it again. Some experts give general advice on smart meter batteries to do this about every 30 charges, but that should be varied according to how much use the bike gets. Someone who empties the battery every weekday commute may only need to do it about once in six months, so about every 150 charges, while someone who only charges their little used bike's battery 20 times a year may need to do it every 10 charges.

Basically it's done when it appears from the mileages achieved at certain content readouts indicate the meter is drifting out. However, it shouldn't be forgotten that battery performance drops in very cold weather as in winter, so a reset then isn't advisable since it may then achieve nothing.

The sophisticated batteries mentioned also have a sleep mode which shuts down their BMS after the battery hasn't been used for about two weeks. This prevents the discharge to run the BMS, and since lithium cells don't self-discharge it means the battery doesn't have to be recharged every two months or so in storage. Recharging after long storage wakes up the battery for further use.

So yes, these batteries are expensive, but they do have valuable features to justify at least some of the cost and they do last well. Some members are using theirs daily well into the fourth year now.
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mountainsport

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In what price region are we talking about? I do not mind paying a fair high price once the quality and technology is there, to keep me on the move for as long as possible. At least people like yourself along with other people on here know what to look out for, whilst others including myself just have to take it or leave it and that hurts.

MS.
 
D

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At least people like yourself along with other people on here know what to look out for, whilst others including myself just have to take it or leave it and that hurts.

MS.
Ignorance is bliss - trust me. This little knowledge is already causing you to worry, when there's nothing to worry about.
 

Tor Atle Lunde

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Oct 5, 2011
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My 2012 Bosch battery died over the winter. The battery was fully charged when put away, and I checked the LED gauge 3 or 4 times during that time but found no reason to charge further. It dropped from 5 to 4 LEDs.

The battery would still perform half decent on flats but when asked to provide more current it would go from full to empty in just a few minutes. After a good rest it could be back to 3-4 LEDs again.

I have always put the battery on the charger after a ride and during the winter it was stored in room temperature. The only other thing I can think of is that the battery has seen a lot of rooty/rocky trails, so it's been well shaken :) I think I recall hearing that some batteries don't like that.
 

flecc

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Oct 25, 2006
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In what price region are we talking about? I do not mind paying a fair high price once the quality and technology is there, to keep me on the move for as long as possible. At least people like yourself along with other people on here know what to look out for, whilst others including myself just have to take it or leave it and that hurts.

MS.
As d8veh says. don't worry about it, if you haven't got one of the bikes using those "smart" batteries you don't have the choice anyway, and very few of the ebikes are using them.

There's an added complication anyway. The Panasonic units using these batteries have a very sophisticated battery usage management which gives the batteries an easier time than most, so that in part accounts for the longer life. Take one of those batteries and use it on a powerful hub motor bike and it won't last as long, I can think of bikes which would probably knock big lumps off their lives.

So whether to use all those advanced battery features is more a decision for ebike and ebike motor manufacturers, rather than part of the after-market.

As for prices, it's difficult to be specific since they vary in different markets. In Britain for example they can be as high as this:

Panasonic for their units: 36v 8Ah = £435; 36v 14Ah = £695

BionX: 36v 9.6Ah = £1050

Buying online from Germany through ebay can cut those somewhat, but still leaving them expensive. By buying generic Chinese batteries you can slash those quoted costs to around a third or less, and good Chinese batteries will last more than a third of the above quoted one's lives.
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103Alex1

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Sep 29, 2012
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My 2012 Bosch battery died over the winter. The battery was fully charged when put away, and I checked the LED gauge 3 or 4 times during that time but found no reason to charge further. It dropped from 5 to 4 LEDs.

The battery would still perform half decent on flats but when asked to provide more current it would go from full to empty in just a few minutes. After a good rest it could be back to 3-4 LEDs again.

I have always put the battery on the charger after a ride and during the winter it was stored in room temperature. The only other thing I can think of is that the battery has seen a lot of rooty/rocky trails, so it's been well shaken :) I think I recall hearing that some batteries don't like that.
With all these things, there's hundreds of possibilities: bad soldering; vibration breaks wire; weld broken on cells; connector not plugged in properly; leaking cell; dodgy fuse connection; broken fuse; etc, etc.

Whatever it is, simple measurements with a voltmeter should soon pin down the cause of the problem. Most causes can be fixed for no cost.

Batteries often play dead, but are not actually dead. I've looked at about 12 "dead" batteries. Only two remain dead because of leaking cheap cells. One needed a fairly sophisticated repair, but the other nine had simple to fix problems.
 

flecc

Member
Oct 25, 2006
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Serious ? :eek: ... that's such a rip-off it's hard to comprehend.
Yes, seriously Alex. In fact it went to that price over two years ago. They come in a fancy case and are very good batteries though, but at that price they need to be!

Battery prices are the number one reason why Bionx don't sell well over here. Actually their prices are just as high in the USA, but for some reason it doesn't affect them as much there. Possibly enough affluent people who don't have to worry about costs.
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trex

Esteemed Pedelecer
May 15, 2011
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My 2012 Bosch battery died over the winter. The battery was fully charged when put away, and I checked the LED gauge 3 or 4 times during that time but found no reason to charge further. It dropped from 5 to 4 LEDs.

The battery would still perform half decent on flats but when asked to provide more current it would go from full to empty in just a few minutes. After a good rest it could be back to 3-4 LEDs again.

I have always put the battery on the charger after a ride and during the winter it was stored in room temperature. The only other thing I can think of is that the battery has seen a lot of rooty/rocky trails, so it's been well shaken :) I think I recall hearing that some batteries don't like that.
I can confirm that rocky trails can damage your battery because it happened to me. The best casing I found is from Ping, the inner hard shell is suspended inside outer hard shell. May be that contributes to their reputation as a quality battery supplier.
 

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