[Closed] re awakening a dead li-on battery

The battery will have a protection circuit between the Li-ion cells and the connector, which controls charging and discharging. If it won't charge (and the charger is set to the right voltage), you're a bit stuffed as the protection circuit has cut out for some reason.

I reckon the kiss of a handsome prince is required.

has not been used for a long time. I went to charge it but it wont charge.

It's knackered.

New battery time.

I'm with Mrmonkfinger, go talk to [url= http://www.mtbbatteries.co.uk/ ]mtbbatteries[/url]

All lithium chargers will refuse to charge a bettery of the battery voltage is below a certain low limit.

You just need to manually force some charge into the battery to bring it's voltage up above the minimum voltage limit.

How you do this depends on the battery, my prefered way is to open the battery case up in order to expose the main terminals on the cells then connect up a variable DC powersupply directly. I just set the voltage so it puts a few hundred mA in and leave it for a while. The disconnect and try the proper charger if it still doesn't charge then carry on with the manual charge for a bit longer.

Done carefully there is very little risk of anything going wrong, but lithium battery's are volitie and can go bang spectacually if you do something daft.

All lithium chargers will refuse to charge a bettery of the battery voltage is below a certain low limit.

Normally because Li-ion cells don't recover once their voltage goes below a certain level, the cell is normally dead.

Only if its been completely drained, which is highly unlikely in this case.

Without trying you just don't know.

Li-ion should never be discharged too low, and there are several safeguards to prevent this from happening. The equipment cuts off when the battery discharges to about 3.0V/cell, stopping the current flow. If the discharge continues to about 2.70V/cell or lower, the battery’s protection circuit puts the battery into a sleep mode. This renders the pack unserviceable and a recharge with most chargers is not possible. To prevent a battery from falling asleep, apply a partial charge before a long storage period.

Battery manufacturers ship batteries with a 40 percent charge. The low charge state reduces aging-related stress while allowing some self-discharge during storage. To minimize the current flow for the protection circuit before the battery is sold, advanced Li-ion packs feature a sleep mode that disables the protection circuit until activated by a brief charge or discharge. Once engaged, the battery remains operational and the on state can no longer be switched back to the standby mode.

Do not recharge lithium-ion if a cell has stayed at or below 1.5V for more than a week. Copper shunts may have formed inside the cells that can lead to a partial or total electrical short. If recharged, the cells might become unstable, causing excessive heat or showing other anomalies. Li-ion packs that have been under stress are more sensitive to mechanical abuse, such as vibration, dropping and exposure to heat.

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

I love this forum, you offer a solution to a problem that your done before loads of times with succees every time and get shot down with a copy paste

Op the approved solution appears to be throw money at it and buy a new battery.

This is all v interesting.

Just out of interest - how long does it roughly take for a stored battery to go from full charge to below the threshold for charging?

If a battery doesn't get used all summer for example, are you going to be in trouble in the autumn?

I love this forum, you offer a solution to a problem that your done before loads of times with succees every time and get shot down with a copy paste

Maybe you should read the post first?

The copy and paste confirms what you said.

The battery protection cuts out at 2.7v but the cell is probably ok down to 1.5v.

If a battery doesn't get used all summer for example, are you going to be in trouble in the autumn?

If the battery is healthy, years. Li-ion self discharge is very low.

Edit: 5% in 24h, then 1-2% per month (plus 3% for safety circuit)

Ok - thanks.

Thank for the posts, I shall try the jump start method. I susspect it went into the cupboard with very little charge and then not used for 6 months. Battery is also pretty old

Apologies. I did read it all and although the first half agrees with me I thought the point of the post was the final paragraph.

If you use my method the key points are

1. You need to bypass any protection circuits built into the battery and
2. Don't try and force a large current into the battery. Just take it nice and slow
3. Don't leave it unattended !

So, not for the non-technical then?

Its already been said, yes the cell might chemically still be viable, but are you going to bet on that - or do you give the safe advice, i.e. new cell?

The non technical 100% will work option is the new battery.

In this case based on what the op has told us I'd put money on the battery being OK. If you're confident in your ability to take the thing apart you haven't really got anything to loose. As if it turns out the battery is knackered you need to buy a new one anyway

Personally I've had quite a few battery packs where one cell has just died, but it still charges fine, but discharge much faster (as they've lost a cell) and don't maintain the correct voltage. Normally the dead cell just stays around 1.2v and never gets above (or below) that.