Battery or Charger?

[Ajax]

I've got a bulb battery, 36v 9amp. When fully charged and still plugged into the charger, the 5 lights on the battery are all shown lit, however after the charger is unplugged, only 4 lights are lit. My question is this, is the battery fully charged? Should all 5 lights be lit?

If the fault is with the charger, 42v 2amp, is there likely to be a simply tweak, something that one can do to the charger's electronic, for it to fully charge the battery?

Put another way, how does the charger know when the battery is fully charged?

 

[flecc]

If it's a lithium battery, the internal BMS circuit balances the cell charges and when they are all full, the BMS cuts the charge receipt and the charger then automatically stops trying to charge.

The battery's meter may have lost it's zero point to measure from, so do a full conditioning cycle. That means riding it to as empty a battery as possible, then fully charging it. Getting it to empty resets the meter zero content point. The riding to empty it doesn't have to be all at once, it can be in separate stages if more convenient. Do not under any circumstances be tempted to discharge the battery any other way, that can wreck it.

If that doesn't solve the problem, it's likely that a cell is a bit down and cannot hold a completely full charge voltage. Since the meter works by measuring the voltage, being slightly down can lose one LED. That won't be lost while it's charging since the voltage from the charger is keeping it on then.
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[Ajax]

Thanks for the advice. the battery has been as close to zero as its allowed to go, and cut to save itself from damage. The lights on the meter were 4 before, and remained the same after. I might still give this a try, however i did come across the following:

"What is conditioning a battery?

This is like excercising the battery.
Don't. This is not appropriate for modern batteries. You will stress the cells for nothing if you run the batteries down to the last 20% of its capacity because the BMS can no longer function."

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