[Ham-Computers] Testing laptop battery

[jandlmiller at bellsouth.net]

Brian, I hope this addresses your concern.  First of all, I make the assumption that the size of battery has been properly matched to the power requirements of the laptop.  This may be a fallacy, but may be as valid an assumption as any of us can make.

With a new, fully charged laptop battery, I test the discharge time with an aluminum heat sink I rigged up that is about 5x7 inches.  Wedged into the fins on the heat sink are five ceramic resistors, each 2 ohms at 10 watts, so that the plus side of the battery is discharged through each of two series of five resistors each.  I use a meter to see the discharge, paying attention to my assumed low limit, after which I stop the discharge and commence charging.

This activity may be more important in imposing one or two deep discharge cycles for a new battery to "condition" it, rather than for any other purpose.

When I am compelled to use a battery in the laptop, because 120VAC is not otherwise available, and for the kind of things I do, I rarely discharge the whole battery.  Sometimes laptops have circuits that tell you in percentage approximate how much battery power in percent remains.  I always have felt that this indicator was dicey at best, but that's all we have.  So, when I think I have too little charge in the battery, onto the heat sink it goes for a safe discharge and then I commence a recharge.

Whenever possible, I pull the battery out of the laptop so that I am not continually putting a charge on the battery (because my theory is that this hastens battery failure), and operate with a small APC 120VAC UPS that prevents data loss in the event of 120VAC failure, and gives me plenty of time to shut down the laptop in a normal fashion.  A good share of my travels enable the use of 120VAC for the UPS.  For the laptop batteries sitting on my shelf, I discharge them and recharge them once a year, whether I need to or not.

Many of my batteries have lasted for many, many years.  They all are expensive, and I wouldn't care if I never had to replace one of them.  I hope this helps you.

John W0IKT