Laptop power from boat batteries

[pteron]

Leaving the laptop battery installed if you're powering from an external source is a very bad idea. Li-Ion batteries are designed to operate in defined cycles: run them down to a specified level, and only then re-charge them.
But if you keep 'topping them up' from an external power source, their working life will be reduced significantly.

I'm afraid this is exactly wrong. In the case of Li Ion batteries they should be kept topped up, just like lead acid batteries.

The major issue with lifetime reduction in laptop batteries is the heat that the laptop generates.

 

[noelex]

I'm afraid this is exactly wrong. In the case of Li Ion batteries they should be kept topped up, just like lead acid batteries.

The major issue with lifetime reduction in laptop batteries is the heat that the laptop generates.

For the longest storage life Lithium batteries should ideally be kept around 50% soc ( some experts advocate 40%, but its not critical around this level) and cool.
Low charge rates are very bad for storage, but high soc is also detrimental.

Self discharge is low for these batteries at cool temperatures, but if the battery is to be be stored or a long time starting with a slightly higher soc, say 60% is sensible.

 

[pteron]

For the longest storage life Lithium batteries should ideally be kept around 50% soc ( some experts advocate 40%, but its not critical around this level) and cool.
Low charge rates are very bad for storage, but high soc is also detrimental.

Self discharge is low for these batteries at cool temperatures, but if the battery is to be be stored or a long time starting with a slightly higher soc, say 60% is sensible.

It is pointless storing lithium batteries - even in optimal conditions they deteriorate. Hence you should never buy old stock of lithium batteries.

My point was related to usage - you will get significantly more life out of the battery if you keep it topped up than if you deeply discharge it.

(you almost certainly have or know someone with a portable device with a charger designed and manufactured by my company)

 

[KellysEye]

What we use to do that is two pieces RadioShack USA/Tandy in the UK kit. A 12 volt car lighter plug (obviously you need the socket) which is on the end of a150W invertor. We weren't sure if you could use the 'box' on your computer cable. So Tandy also sell a cable and 'box' for computers that can be adjusted from 12v to 24v. That plugs into the invertor. If Tandy don't sell those have a look at the Radio Shack site.

 

[alisdair4]

240v monitors on 12v

Without trying to drift this thread, (he typed, drifting the thread!) can I pose a question of the experts related to monitors? I would like to use a netbook with the lid down, tucked away in the chart table (and thanks to the Windows experts, I now know how) feeding an external monitor. Is there any reason why I should not apply the same method (12v adapter, DC to DC) to power the monitor? FWIW, the adapter for monitor I am considering using has an input of 100-240v, 1.7A, and an output of 12.0 v DC, 5A. Or would I be safer using the existing coke-can invertor for the monitor, and powering the netbook from a Maplins (or similar) DC to DC adapter?

 

[Amulet]

For the longest storage life Lithium batteries should ideally be kept around 50% soc ( some experts advocate 40%, but its not critical around this level) and cool.
Low charge rates are very bad for storage, but high soc is also detrimental.

Self discharge is low for these batteries at cool temperatures, but if the battery is to be be stored or a long time starting with a slightly higher soc, say 60% is sensible.

Yep, that's what I learned at school - well actually from reading as an old geezer. 40% charge in the fridge - not much help when you're trying to use them.

 

[noelex]

Yep, that's what I learned at school - well actually from reading as an old geezer. 40% charge in the fridge - not much help when you're trying to use them.

My point was related to usage - you will get significantly more life out of the battery if you keep it topped up than if you deeply discharge it.

You can still use them and keep them roughly at this level of soc. The important thing is to avoid low discharge but also try not to keep them close to fully charged.

Our Lead acid boat batteries are best at 100 - 50 % soc. The optimum is 100%.
in a similar way if you want a long life out of lithium keep them in the 80 - 30% range. The optimum is 50%.

This is not always possible, but it's nice To know what to aim for.

Lithium batteries can be expensive, particularly for devices like the iPad where replacment involves removing the screen etc. On other products, like some mobile phones, cheap replacment batteries are available and can simply and inexpensivly be exchanged. The level of care of the batteries should reflect the cost and inconvenience of organising a replacment.

For some devices there are applications that will keep the charge level within whatever parameters you prefer.

 

[pteron]

But then you give away run time.

There are techniques used by more sophisticated chargers that modify the charging procedure to give both capacity and cycle life. It is possible to observe the damage occurring and adjust to ameliorate it.

If you don't intend to use the battery then allowing it to sit at a lower SOC will of course prolong it's life, but I have a portable device because I want to move around with it. Under that usage case, it is better to have many short discharge/recharge cycles than allowing it to run down completely.

The termination voltage is chosen to balance the competing requirements of cycle life and usage time. The power management in a modern portable device is a sophisticated beast backed up by significant analysis of the behaviour of the particular battery cell in use. You will not beat its ability to look after the battery by attempting to second guess it.

 

[noelex]

The battery settings are designed to simply charge and hold the battery at 100%. The IBM thinkpad laptops had a setting called " maximum battery health" which stopped the charge at 80%, but this sort of feature is rare.
There is nothing wrong with charging the battery to 100% , but it's important to realise that 100% is shortening battery life when it will not be needed.
On a lot of products the device will be obsolete or will be replaced before the battery gives out anyway. For other products there are cheap replacement batteries available.

However on some products like iPads, and some laptops battery health can be important. On these devices I try to keep the battery in the 80-30% range where possible. if it is to sit unused for a reasonable time I will stop the charge at about 50%.

Telling people Lithium batteries are like lead acid batteries and need to kept at 100% for maximum battery health is wrong and I am trying to correct that wrong information. I am not trying to stop people charging their batteries to 100 %, because often this is a sensible solution I always charge my mobile phone like this as battery health is not a particular concern.

 

[pteron]

My point, likening them to lead acid, is that unlike Nimh and NiCd, they are better suited to the use and top up regime, whereas the nickel based batteries generally respond better to a deeper discharge and recharge regime.

Believe me, Apple have many battery chemistry experts. If keeping the battery at 50% significantly affected useful life they would be recommending it. But they don't. They have access to the latest Li battery technology and don't need to rely on battery university to tell them how to look after it.

 

[noelex]

My point, likening them to lead acid, is that unlike Nimh and NiCd, they are better suited to the use and top up regime, whereas the nickel based batteries generally respond better to a deeper discharge and recharge regime.

Believe me, Apple have many battery chemistry experts. If keeping the battery at 50% significantly affected useful life they would be recommending it. But they don't. They have access to the latest Li battery technology and don't need to rely on battery university to tell them how to look after it.

The techniques for taking good care of Lithium batteries is well know, it's no secret.
Unfortunatly good advice on how to take care of the batteries conflicts with their marketing aims of claiming a long battery life. They don't even usually warn users of the problems of regularly discharging the battery to when the computer shuts off ( generally at 5-10% soc).

I don't think they really mind selling more batteries either (or in the cases of iPads and iPhones perhaps a new product, because of the cost and trouble of replacing the battery). They often exclude the battery from the general warranty so it is not usually a warranty claim if the battery has a short life.

 

[pteron]

The techniques for taking good care of Lithium batteries is well know, it's no secret.
Unfortunatly good advice on how to take care of the batteries conflicts with their marketing aims of claiming a long battery life. They don't even usually warn users of the problems of regularly discharging the battery to when the computer shuts off ( generally at 5-10% soc).

I don't think they really mind selling more batteries either (or in the cases of iPads and iPhones perhaps a new product, because of the cost and trouble of replacing the battery). They often exclude the battery from the general warranty so it is not usually a warranty claim if the battery has a short life.

There is a huge amount of R&D in the area of Li cycle life and capacity, and the techniques being developed are the life blood of several startups. I assure you they are not generally known.

Regarding your latter point, they are painfully aware of the issue of battery life not meeting customer expectations - they suffered a class action lawsuit because of it.

 

[saltyrob]

Hi ,

Many thanks for the sdvice and am pondering the options.

Rob