No More Twist

NB since writing this I have had some trouble with a grey battery. See here for the sad story!

A notebook computer can last for years but under regular use, the battery can fail in as short a time as a year. Depending on how popular your model is, you can have several options for replacing the battery and restoring the laptop to usability.

The most legitimate option is to buy a new battery from the manufacturer, but it’s no surprise that these are priced at a premium. What you are paying for is reassurance that the product will be the right part for your notebook, that it will be safe and of good quality. Other options include buying from a specialised battery supplier, and these are slightly cheaper. You still get reassurance that it’s the right part – but it might have been in stock for some time and as a result may have lost a significant proportion of its capacity.

You could buy a ‘compatible’ battery from a supplier. This might not have the official markings but will basically work in the same way as an official battery. There are scare stories about exploding and incendiary batteries, but if you read the news this seems as likely to happen with a major brand name battery as an unknown one.

Finally you could buy a second hand battery. I can’t think why you’d want to do this, unless it was to get an end-of-life system up and running so you could sell it on. There are good chances that a second hand battery will be nearing the end of its life. With modern ‘smart batteries’ there are things you can do to test this. Here is what I get when I ask the battery how it’s doing:

# cat /proc/acpi/battery/BAT0/*
alarm:                   660 mAh
present:                 yes
design capacity:         6600 mAh
last full capacity:      6344 mAh
battery technology:      rechargeable
design voltage:          11100 mV
design capacity warning: 660 mAh
design capacity low:     200 mAh
capacity granularity 1:  66 mAh
capacity granularity 2:  66 mAh
model number:            DELL F5
serial number:           578
battery type:            LION
OEM info:                Sanyo
present:                 yes
capacity state:          ok
charging state:          charged
present rate:            1 mA
remaining capacity:      6600 mAh
present voltage:         12550 mV

That was my new ‘grey’ battery. Here is the same info for my original Dell battery at the end of its life:

alarm:                   480 mAh
present:                 yes
design capacity:         4800 mAh
last full capacity:      1365 mAh
battery technology:      rechargeable
design voltage:          11100 mV
design capacity warning: 480 mAh
design capacity low:     145 mAh
capacity granularity 1:  48 mAh
capacity granularity 2:  48 mAh
model number:            DELL F51335
serial number:           4198
battery type:            LION
OEM info:                Sanyo
present:                 yes
capacity state:          ok
charging state:          charging
present rate:            1 mA
remaining capacity:      1242 mAh
present voltage:         12490 mV

And this is the same info from a brand new genuine Dell battery – what you get if you but a new laptop and order the upgraded 9-Cell battery:

alarm:                   780 mAh
present:                 yes
design capacity:         7800 mAh
last full capacity:      7985 mAh
battery technology:      rechargeable
design voltage:          11100 mV
design capacity warning: 780 mAh
design capacity low:     236 mAh
capacity granularity 1:  78 mAh
capacity granularity 2:  78 mAh
model number:             DELLRD8507
serial number:           1938
battery type:            LION
OEM info:                SMP
present:                 yes
capacity state:          ok
charging state:          charging
present rate:            1558 mA
remaining capacity:      7298 mAh
present voltage:         13172 mV

The interesting fields are the design capacity compared with the last full capacity. As a battery gets older it will be less able to hold the charge, so the ‘last full’ figure will fall relative to the original design capacity.

The other test I had for my grey battery was to weigh it – since there are cheap 6-Cell versions and more expensive 9-Cell ones, this will tell you if it has the right number of cells inside.

So my ‘new’ grey battery clearly isn’t quite as good as a genuine Dell battery, but it’s a lot better than my old exhausted one.