Battery woes

[awol]

Cycling into a 30mph head on wind the other day has give my battery a beating. At 18mile it died where I have in the past had 30miles. Not to worry I give it a good charge up for the next day, but I noticed a considerable lack of power even though the volts on my handlebar volts display appeared ok. I give it a full charge again and still a lower umph.
Opened it up this eve and took volt readings between the b- and each connector wire on top.
I get 3.8 - 3.8 - 3.9 - 3.9 - 3.9 - 3.9 - 3.7 - 3.8 - 3.9 - 3.9
Do the readings look ok or is the 3.7v a bit too low and need charging a bit?
If all looks OK then is it a case of it's just on it's way out?

 

[Deleted member 4366]

It looks too low. You need to charge it up, check the voltages again, then discharge and re-check to see what's going on. What battery is it?

 

[awol]

Cheers d8veh,
It's a bmsbattery 10ah bottle done about 280 charges.
I have put that single connection on charge with my BC168 with the minus on that pin and the plus on the pin next to it and it's going fine, or did you mean charge up the whole pack? If so I can go and do that instead.

 

[Deleted member 4366]

That's OK. Use the BC168 to make them all equal at somewhere between 4.15v an 4.2v, then run the battery down and check the voltages again before re-charging. That will show if that cell has lost capacity.

 

[awol]

That cell has now held at the same volts as the others, they are all now about the same after a 10miles run, so I will try the 20mile run I normally do tomorrow to check if I get it. If I get the 20miles I will leave the battery for now with slightly less umph until it starts loosing too much power. I presume any weak cells identified will need exchanging which I will leave as a last resort.
I don't really know how to charge the other cells with the BC168 as the volt readings seemed to come from random pins and not in order so if I need to do that in the future I will draw a diagram with readings on it and request help from that. Thanks.

 

[Deleted member 4366]

The 10 readings swap from side to side on the BMS. I cant't remember the exact sequence, but it goes something like 1, 4, 5, 8, 9 on one side and 2, 3, 6, 7, 10 on the other. You'd have to make a special lead. I use the pins from pin header strip soldered to a normal 6S connector for the BC168, but whatever you do, don't let the pins touch each other while the BC168 is charging otherwise it's voltage sensing changes so that the voltages displayed and charged to are incorrect.

I'm sure half of the problems with these batteries are from water getting in. Did yours get wet any time?

 

[awol]

Thanks for that d8veh, telling me that sequence made me realize it's not random and is worth some concentrating on and you were pretty close when I worked it out with a diagram.
Mine is 1-3-6-7 one side and 2-4-5-8-9-10 the other.
So I rigged up my load bank of watt meter,kettles,soldering irons etc to get up to a 4.7a load. With battery 1/2 empty ish
no load readings
3.75 3.77 3.77 3.77 3.78 3.78 3.75 3.72 3.79 3.78
and with 4.7a load
3.61 3.62 3.61 3.58 3.59 3.58 3.47 3.52 3.59 3.56
Is it best doing that sort of test with a flat battery as appose to 1/2 full? or can you tell from these readings if it is worth any further action other than it's all worn out?

 

[Deleted member 4366]

That doesn't look too bad apart ftom cell 7, which is a bit saggy. I don't think that there's much more you can do with it. It's very tricky to replace any cells unless you have a tab welder. I think you just use it as it is until it expires. Maybe use the oppotunity to upgrade to one of those bigger downtube batteries. It's only money.

 

[awol]

Thanks, I will go for charging at both ends now and see how much longer I get out of it until it won't even manage that.
Can't upgrade the battery at the moment but I do have a bmsb 20ah 'breeze block' which is too heavy for me but I will now have to start using more and will look at using my rc lipo's idea now too.