SparkFun Forums

[angelsix]

I've just brought another laptop and checked out the battery life (still only 3 hours as its a power laptop)

I took a look at the specs and it states 11.5V 3500mA/h... now surely they would be more than that?

This got me thinking... if that is all they supply, could I not just series together 10AA batteries (2200mA/h) and get 22A hours and effectively increase the life by almost 10x.

Obviously I would take it further and instead use rechargables and not go directly to the battery supply but instead perhaps go in at the plug side (19.5V) and put 20 batteries in series through a switching regulator and output at the 19.5V so that as the batteries drain and the voltage drops it would still output 19.5V and be regulated?

I presume I am misunderstanding some part here as I really cannot see why if it were so simple laptops do not come with much higher capacity batteries? For the size of the battery they have they could fit 12 AAs in series not a problem there. Not sure how well rechargable AAs last though and perhaps that is the issue?

Just a thought anyway, anyone have any obviously reasons why this wouldn't work?

[waltr]

I think your battery math is a bit off.
If a 3500mA-hr battery lasts 3 hours then the laptop to drawing 3500/3 = 1.166Amps average. Therefore a 2200mA-hr battery would only last for 1.88 hours (2200mA-hr / 1166mA).

[Gsm Man]

could I not just series together 10AA batteries (2200mA/h) and get 22A hours and effectively increase the life by almost 10x.

Putting the batteries in series increases the Voltage not the Current. You are still only going to get 2200mA/hrs.

[angelsix]

Ah right thought something must be off, ye so the current is not going to increase obviously.

So, on to plan 2. Are there any really high current batteries that I could use that are about the size of a laptop battery? My plan is to have a "spare" battery I can have at the side of the laptop while out to have the battery last longer.

[NleahciM]

Lithium-polymer batteries have the highest energy density (both in terms of joules/liter and joules/kg) right now of the commonly available chemistries. Your current battery pack is lithium-ion, which is slightly worse in both specs. However, li-ion cells are not as prone to things like fire, so you may want to take that into consideration.

I think you'll find it easiest to try to plug your homemade pack into the DC in jack, as opposed to the battery connector, so your computer will act as if it is on wall power and probably not run as efficiently as it would on just battery power.

[teekay_tk]

cheaper and easier would be to buy a second hand battery from ebay. Making a new lithium Polymner pack will be more expensive. Yes it wont be that much fun. But laptops are more expenive so it is a big risk to make your own barrey backup

[gmarsh]

I've used three 6V SLA batteries in series to power a laptop though its DC jack. Worked decently.

[stevech]

My new Dell laptop has a big battery, (purchase option) almost as large as the laptop in length and width, and about 1/2 inch thick. It clips onto the laptop and provides power via the docking port.

With it and the oversized built-in battery, I get 6-8 hours.

I also have a 2nd battery for the internal plugin one. With the big flat battery in place, I can also swap the internal without rebooting.

[esklar81]

There are commercially available, multi-device external battery packs, such as:
http://chinagrabber.com/cheap-2000mah-u ... b2000.aspx

I have such a device (but not the one at that link). I point out that the one at the link claims 20,000 mA-hr, but does not say at what voltage. It could well be, for example, that it has six LiPo cells, each of 3334 mA-hr, rated at 3.3 V. Such a set of cells would have 20,024 mA-hr at 3.3V (if arranged in parallel), but only 3334 mA-hr at 19.8V when (if arranged in series).

Eric

[macegr]

You can get portable "jump boxes" that are used to jumpstart a car without having to get another car and the jumper cables. Very handy to have around. Anyway, a lot of them also have AC inverters and cigarette lighter jacks you could use to power your laptop. Usually 18,000 mAH and there's probably inefficiency in the DC conversion process, but it'd probably power the laptop twice as long as the internal battery would, and also be useful for other things (like starting cars!).

[astinsan]

They sell large packs by apc that will strap to your laptop or plug in to the back of your laptop with enough power to last several hrs.

If you build your own pack you have to link cells in paralleled circuits to give enough amperage then link in series to get enough voltage. You would also need to make a regulated output. You also have to keep in mind that some batteries don't charge well in parallel (nimh). There was a hackaday on this subject. You should see if you can find it.