Is My Battery Dying ?

[Del 80]

Just been out on the Batribike Granite.......first time for ages, after about a mile the battery was showing three bars......then cut out all together......got back to base camp in normal pedal mode, and the battery is now showing fully charged......is my battery dying? or could there be another reason?.........

 

[Tony1951]

Just been out on the Batribike Granite.......first time for ages, after about a mile the battery was showing three bars......then cut out all together......got back to base camp in normal pedal mode, and the battery is now showing fully charged......is my battery dying? or could there be another reason?.........

I had similar effects when one group of cells in my battery was out of balance after a seven month winter lay up. I did check the overall voltage regularly during the winter and it never went below about 36v (it is a 36 volt battery) but I think it would have been better to charge it regularly. Then the BMS might have been able to keep the cell groups in balance, but after seven months off - the difference was far too great for the BMS to deal with.

Anyway - on opening and examining the battery, one cell group was low - way out of balance - about 3.6v when the others were fully charged at about 4.2v. The BMS was shutting the output off to prevent over discharge of the weak group. The battery has ten parallel groups and when fully charged it shows 42 volts.

In use, this group of cells was dropping to the BMS shut down voltage long before the other groups were any where near depleted. I manually charged the low group so it matched the rest of the cell groups, and it has behaved itself ever since. It may be that one of the cells in the low group is slowly leaking its charge and dragging down its parallel cell group over the months of disuse.

In your case, I would charge up the battery fully, measure the overall voltage and note it down. Then run the bike and see if it happens again.

If the problem continues after charging, you will need to deal with it, or get someone to do it for you. If you are not experienced in such matters be very careful. There is a lot of power stored in there - all waiting for a short circuit or bit of mishandling to make very big sparks and hot metal.

 

[Bikes4two]

It does sound like your battery is just holding a surface charge - once under load, that charge soon evaporates and you end of with now useable power.

Others will be along to suggest some possible first aid measures that might help recover the battery.

There's always the possibility of the BMS playing up but knowledge of these devices and your particular battery are beyond my ken.

 

[Del 80]

I had similar effects when one group of cells in my battery was out of balance after a seven month winter lay up. I did check the overall voltage regularly during the winter and it never went below about 36v (it is a 36 volt battery) but I think it would have been better to charge it regularly. Then the BMS might have been able to keep the cell groups in balance, but after seven months off - the difference was far too great for the BMS to deal with.

Anyway - on opening and examining the battery, one cell group was low - way out of balance - about 3.6v when the others were fully charged at about 4.2v. The BMS was shutting the output off to prevent over discharge of the weak group. The battery has ten parallel groups and when fully charged it shows 42 volts.

In use, this group of cells was dropping to the BMS shut down voltage long before the other groups were any where near depleted. I manually charged the low group so it matched the rest of the cell groups, and it has behaved itself ever since. It may be that one of the cells in the low group is slowly leaking its charge and dragging down its parallel cell group over the months of disuse.

In your case, I would charge up the battery fully, measure the overall voltage and note it down. Then run the bike and see if it happens again.

If the problem continues after charging, you will need to deal with it, or get someone to do it for you. If you are not experienced in such matters be very careful. There is a lot of power stored in there - all waiting for a short circuit or bit of mishandling to make very big sparks and hot metal.

 

[Del 80]

Very interesting reading Tony, thank you......got battery on charge now, will see what happens.....I don't know how old it is, or how long it's been laid up.....if it happens again, I will take it apart and have a look......

 

[Del 80]

nd like your battery is just holding a surface charge - once under load, that charge soon evaporates and you end of with now useable power.

Others will be along to suggest some possible first aid measures that might help recover the battery.

There's always the possibility of the BMS playing up but knowledge of these devices and your particular battery are beyond my ken.
[/QUOTE]

 

[Del 80]

Thank you......it surprised me that it went so low that it didn't even register that the battery had gone completely flat.......work in progress......

 

[Bikes4two]

Hi @Tony1951

...... I manually charged the low group so it matched the rest of the cell groups, and it has behaved itself ever since. ...

What did you use and how did you manually charge the low group please?

 

[Del 80]

O.k......With the battery fully charged, it gives a reading of 41 volts.....just going for a run on it, and will see what it says when I get back........

 

[Del 80]

O.k......With the battery fully charged, it gives a reading of 41 volts.....just going for a run on it, and will see what it says when I get back........

Just been about 3 miles, and taken another battery reading.....39 volts......I wonder if the old girl has been laid up for too long, and it will take a while for the battery to "settle down"......now got it on charge again........

 

[Nealh]

41v indicates and issue either tired cells or one group is low, one should see at least 41.5v for healthy battery.

 

[Del 80]

41v indicates and issue either tired cells or one group is low, one should see at least 41.5v for healthy battery.

Fully charged again, and reading 42 volts this time.......another run out tomorrow, with some hills involved.........

 

[Bikes4two]

• Are you using a fairly decent volt meter/multimeter - hopefully one that measures to a least one decimal point?
• The drop from 41v to 39v after 3 miles isn't great but promising.
• Ideally it would be a handy diagnostic measure to see how much the voltage drops when you put the motor under load.
• How much of a voltage drop under load you get is to some degree dependant on the specific battery cells used and I've no particular experience in this respect - maybe others like @Nealh could advise in this?

 

[Nealh]

Voltage drop and sag are very different, one shouldn't confuse voltage sag that rebounds and voltage drop that doesn't, the latter is more serious and more of a guide to the battery health.
One ideally needs a lcd display that registers the live voltage in use.
That said if a cell sags badly and still rebounds to SOC (state of charge) then, it can be deemed a poor quality cell that can't handle current draw very well.

Cell age & brand, current draw and parallel cell numbers can determine how much sag there may be but with voltage drop it is a different story. A drop in voltage is one that doesn't rebound to SOC, if the drop is over only 3 miles one sees 2v in difference then the battery sounds weak to me. One can expect the first 0.5 - 1v to drop quite soon within a mile as the top charge of a cell between 4.1v - 4.2v holds very little capacity, but after this any voltage drop should be a lot slower.

With my LG hg2's I see 0.3 -0.5v sag in low PAS which is 2.6 - 4a, though I am only using 2 cells in parallel and towing a laden trailer. As soon as the current draw lessens then the voltage rebounds to it's SOC, which is normal with all batteries.
If I were using more cells in parallel 4 - 6 cells then I would see much less sag, for my use 30 miles range is fine so 2 parallel cells makes for a lighter/smaller battery and only 3 hrs to charge from lvc.

 

[Del 80]

Voltage drop and sag are very different, one shouldn't confuse voltage sag that rebounds and voltage drop that doesn't, the latter is more serious and more of a guide to the battery health.
One ideally needs a lcd display that registers the live voltage in use.
That said if a cell sags badly and still rebounds to SOC (state of charge) then, it can be deemed a poor quality cell that can't handle current draw very well.

Cell age & brand, current draw and parallel cell numbers can determine how much sag there may be but with voltage drop it is a different story. A drop in voltage is one that doesn't rebound to SOC, if the drop is over only 3 miles one sees 2v in difference then the battery sounds weak to me. One can expect the first 0.5 - 1v to drop quite soon within a mile as the top charge of a cell between 4.1v - 4.2v holds very little capacity, but after this any voltage drop should be a lot slower.

With my LG hg2's I see 0.3 -0.5v sag in low PAS which is 2.6 - 4a, though I am only using 2 cells in parallel and towing a laden trailer. As soon as the current draw lessens then the voltage rebounds to it's SOC, which is normal with all batteries.
If I were using more cells in parallel 4 - 6 cells then I would see much less sag, for my use 30 miles range is fine so 2 parallel cells makes for a lighter/smaller battery and only 3 hrs to charge from lvc.

Thanks for that.....sending son (fitter than me) out on it tomorrow.....he has instructions to go about 10 miles.....will see what happens.....to be honest I think a new battery is called for.....unfortunately batteries for this particular model are no longer available, so may have to shop around for a replacement.....

 

[Nealh]

If the battery connection is simple two wire only then one can use any generic battery of the correct voltage, however I'm not 100% sure if they haven't used a CANbus sytsem before or not on some bikes. If so any replacement will be expensive.

 

[Tony1951]

Hi @Tony1951

What did you use and how did you manually charge the low group please?

Late response - sorry.

Having found the low group, I soldered two charging wires onto the nickel strips at the positive and negative ends of the group that had a lower voltage, avoiding any heating to the actual cells by just tagging on the wires between the cells. I then connected these leads thus installed to a small lithium 4.2v charger, which I knew would cut off at 4.2 volts, and waited many hours for it to charge to the same level as the other groups.

The battery seems to have held up pretty well since then and though it has not been heavily used since, has done about a hundred miles and the problem has not recurred.

I think it is clear that that cell group probably contains a cell with some internal leakage, otherwise, I can't see why a 7 month layup period would lead to the balance problem arising.

My strategy for living with that, will be to make sure I use it next winter and charge it to full on a regular basis. My reasoning on the regular re-charge plan is that the BMS will be able to manage balance issues that are not great, whereas letting it develop to what it was last winter puts the imbalance way beyond what the BMS can deal with.

 

[Del 80]

O.k......No. 1 son has just been out on the bike.....voltage on leaving 4.1 volts......went about five miles, on the flat, in 5 th gear......voltage on returning 4.1 volts......maybe all is not lost ?