Definitive Battery Extender Guide Rev. 2.10

Battery Extender for HP Jornada 928

Dear Adrian,

I am a HP Jornada 928 user, and was so frustrated with the battery life that I started thinking of the extender.

I remember I used to builded my first extender for my walkman as a teenager using a bicycle torchlight holder.

Alas, that was because I have no knowledge of ampere and simply extending the battery life from a AA battery to a A battery.

Your webpage is really useful and has given me the zest to want to give it a try.

Just a quick question about the Ampere-hour rating.

The adaptor to the PDA reads 5V 1.7A.

I know that I can put 3 AA batteries in series to get 4.5V, but one thing that puzzles me is will a higher ampere reading “burn” anything?
e.g. a alkaline battery has a 2A reading, though in series, the ampere will still be 2A

While waiting for your reply, I did some calculation and toying with my multi-meter. And decided to go ahead with cutting the adaptor up for the plug in. I shopped for a 3 batteries torchlight that cost A$3.50. (errr sorry I don't know how to attach picture here, will send you by email)

Now, I have the following question:
1) the charger light on the PDA start blinking when I turn it ON, but indicate charging when it is OFF
2) When the indicator shows that it is fully charged "Blue light", it is not actually fully charged
3) for example, it was 64% charged before I put in the extender, after connecting the extender for some time and it indicated 72%. However, immediately after I turn it ON by opening the cover, it jumps right back to 64%

What did I do wrong??

I would really appreciate your time and advice please. And patience too as this is the first time I join a disscusion forum.

Yours sincerely,

Benjamin

 

no charging

Tested the extender for a whole night.

It didn't charge the PDA batttery. However it maintain the potential voltage. I suspect that it is becasue the extender potential is 4.5V where the required is 5V. So it only managed to "maintain" instead of chraging because it is lower in potential.

Really exciting, will look forward to your reply.

Until then, I will try to source out a 4 batteries holder to connect it with 4 x 1.2V rechargeables (5V).

The current don't seems to be creating any problems.

This is really good timing, because I will be travelling to Japan, Singapore and Malaysia coming Friday (3 June), so I don't have to worry about losing power.

Thanks Adrain.

 

Why thinking small?

If I'd need more power for a 6V appliance I'd buy a 6V 150Ah heavy duty truck/tractor battery.
That'll cover most needs... possibly except for portability.

If portability is an issue then I'd go for a 7Ah motorcycle battery.

Cheers
Olle

 

This means that it will be at 5V when the current is 1.7A. Most likely the voltage is higher at lower amps.

The "reading" is irrelevant. Higher voltages will create higher currents, and those currents can cause problems.
In your case the voltage is below the rated 5V, so no risk of damage!

No. With batteries in series the voltage will increase while the charge (rated in Ah) stays the same.
With the batteries in parallell the voltage stay low but the charge is multiplied.

Quite normal since alkaline batteries don't carry that much charge to start with. When you turn the PDA on the voltage drops due to the increased current used.

Same phenomenon as above.
The charge indicator reads the voltage. With the PDA off the voltage is "high", but when it's turned on the voltage drops.

/Olle

 

Seems like a better idea. The rechargeable batteries have a better capacity than the alkaline ones.
I still have a feeling that the internal PDA battery is rated at a higher voltage than 5V, and that it's rather 6 or 7.2 volts.

When the PDA battery is given at 40-60% charged, try to measure the voltage at the socket where you should attach the charger.
If there's a voltage it should be the nominal battery voltage.
(When it's fully charged it's 10-30% above the nominal voltage, depending on battery type.)

Cheers
Olle

 

portability is the key

More updates, the AA batteries lasted about a day without the PDA need to be charging.

Thanks for your help, at least I know I can do more with my PDA, I have left it as a paperweight for nearly a year and went back to “pen and paper”.

And thanks Olle, true, the heavy duty batteries are really long-lasting but at the end of the day we are still talking about portable-digital-assitance (PDA) so portability is important.

Maybe soon, we will get solar cells small and strong enough to power the PDAs and phones... can be a great business venture