Improving the CradlePoint PHS300′s battery life

March 30th, 2008


I love my PHS300. Being able to go out and having internet whenever I need it is really liberating. Of course there is one drawback; I’m talking about the battery life. I’ve turned the signal on the PHS down since it’s usually close by. I’ve found that typically I get 90 to 120mins connected time before my PHS300 battery gives up. Battery life is decent but it’s not long enough that I can leave it on whenever I’m out. I have to turn it on whenever I need it and remember to turn it off when I’m done.

When I’m out I usually bring a Toshiba Libretto (a small laptop with a 7″ display) plus the PHS300 and my modem. I carry it all in my man purse.

After reading a thread at EVDO forums, I was inspired to try making an external battery pack for my PHS. Rechargeable AA batteries have a voltage of 1.2 volts. 4 AA’s connected in series would yield a voltage of 4.8 volts which is close to the PHS AC adapter’s 5 volts.


I happen to have tons of AA rechargable batteries lying around from my SLR camera gear and various video game controllers. I have two types of batteries – Sanyo 2500mAh NiMH batteries which are the regular kind that discharge if you charge them and they sit on the shelf for a while. The other kind is Sanyo’s newer ENELOOP 2000mAh NiMH batteries. These have less capacity but only lose 15% of their charge per year (so they claim). Since I’m guessing they will only last a day or two I’m going to be using my 2500mAh cells.

I recharge the batteries with a Maha C801D.

Regular alkaline AA’s have a voltage of 1.5 volts and will fit but I’m not sure if the voltage is too high. I didn’t try them.

Before you read my instructions, here’s my disclaimer. If you break your PHS300 using my instructions it’s not my fault. If somehow you manage to set your PHS300 on fire it’s not my problem but please do send me a picture.

Here’s my instructions on how to make your own external battery pack. They’re actually very simple but in the interest of helping total electrical noobs (like myself) I’m being very very verbose.


  1. Soldering iron
  2. Solder
  3. Multimeter
  4. Heatshrink wrap
  5. 4 cell AA holder
  6. Compatible plug
  7. Wire stripper
  8. AA NiMH battery
  9. Hair dryer


  1. Stick AA batteries into the holder
  2. Strip off some wire from the compatible plug. 1/4″ should do fine. Separate the wires for an inch or two.
  3. Put some small heatshrink wrap on EACH wire from the AC adapter plug. You don’t need that much.
  4. If you want a neater looking job, you can put a thicker piece of heatshrink wrap to cover the parts of wire that are separated.
  5. Connect wires from the battery holder to the compatible plug. Connect the red wire from the battery pack to one of the wires on the compatible plug. Do the same with the black wire and the other wire on the compatible plug. Make sure the 2 sets of wires don’t touch.
  6. Check polarity with the multimeter.
  7. measuring1.png
    1. Here’s how you do it: The PHS300′s plug polarity is like this -c+ the outside is negative and the inside is positive (see the picture above).
    2. Set your multimeter to measure DC voltage, you want it at a resolution that will handle around 6 volts.
    3. While the batteries are in the holder and the wires are connected, place the black tip from the multimeter on the outside of the plug and place the red tip from the multimeter on the INSIDE. Make sure the red and black wires from the battery pack are not touching each other.
    4. tips.png
    5. If the voltage is +5 (around there, mine read 5.2 volts) you’re good to go. If the voltage is negative, the polarity is wrong. Swap the red wire from the battery pack with the black wire from the battery pack and test again to make sure it is now positive.
  8. Solder the red wire from the battery pack with the wire from the AC adapter. Do the same with the battery pack’s black wire.
  9. Wait for things to cool and then move the two thin pieces of heatshrink wrap over the exposed wire.
  10. Use the blow dryer to shrink the wrap.
  11. If you wanted a neater job, move the thicker piece of heatshrink wrap over the two smaller wires and shrink it with the blow dryer.
  12. Check the polarity again. Make sure the voltage isn’t higher than 6 volts.

You’re done! Please note I don’t have any heatshrink wrap in my how-to pictures. I cut the wrap off of my setup to take pictures of it.

Using the new external battery pack I found my PHS battery life went from about 120mins to almost 7hrs. An increase of around 5 hrs. Please note I’m not constantly using the PHS300. A lot of the time it’s on but I’m not. 5 hr’s isn’t bad but it’s not quite enough for a long day. I ran out, got some more supplies and connected two 4 cell AA holders in parallel. Connecting them in parallel is the same as my instructions only you do this differently:

Connect the red wire from battery pack 1 to the red wire on battery pack 2 to the correct wire on the AC adapter plug. Do the same with the black wire from the battery packs, check polarity and solder. I connected the packs using some double sided tape and some parts I had lying around the house.


Now you get the same voltage but double the run time. Now I can get close to around 12 hrs of battery life. That’s good enough for me. If it’s not enough for you to make a battery holder with D cells (D cell NiMH batteries have capacities of around 10000mAh)

Since the battery pack is not that thick I can fit it, my laptop, modem and router in my man purse no problem. Sweet huh?

Howard Chui

Entry Filed under: Latest Accessories,Phones

18 Comments Add your own

    TelecomZombie  |  March 31st, 2008 at 2:25 am

    Nice! Hope no Frogs were injured during the soldering of the connections. :D Batteries&hellip  |  April 1st, 2008 at 1:25 am

    [...] all set to go out when my wife noticed a funny smell. It turns out I put one of the batteries in my homemade PHS300 battery holder backwards. My batteries exploded, my man purse has a nice hole in it and now I’m looking for [...]

    John  |  April 3rd, 2008 at 1:00 pm

    I wonder what you’d have to do to make it such that you could recharge them in the holders, so you could treat it like one sealed power unit (that way you don’t accidentally put batteries in backward when you’ve just recharged a batch :-} ) … and I wonder how to interface with a USB cable too (for charging, or for regular power; I have my phone and PDA both set up to charge from USB adapters on my home and work computers, on a wall outlet in my bedroom, and on a car->USB adapter in my car).

    GameKyuubi  |  April 9th, 2008 at 5:47 am

    What you’d have to do for that is:

    1) Instead of connecting the batteries to the 5v charger jack, connect them to the terminals used to draw power from the battery. In PARALLEL, NOT SERIES. You can actually connect as many 5v modules as you want this way. It will increase the mAh, not the voltage, so it is safe. Just make sure you put them in the right way I guess lol.

    2) Uhh. I guess there isn’t a number 2. I explained just about all of it in number 1. Oh well.

    AC Adapter Guy  |  May 26th, 2008 at 2:53 pm

    That is an interesting project. Maha had a charging pack similiar to that a few years ago, but a little pricier than what you did.. I would not try to rig my own charger if I were you. You would need to regulate the current delivered pretty carefully or you could end up blowing up another battery. Speaking of which, I was surprised that it blew. NiMH hardly ever blow, Li Ion sure but not , (yep my family and I sell them). Anyway congratulations on building the pack and please be carefull, you might want to throw some Shottky diodes in there to prevent another incident…..

    Derek  |  June 10th, 2008 at 12:02 am

    When you say connect the red wire to the red wire to the AC chord do you mean just get the two red wires to end up as one wire going to the connector?

    Maj  |  July 7th, 2008 at 12:22 pm

    You could have done it a lot easier than that.

    The PHS300 uses Kyocera TXBAT10073 batteries which you can get for about $5 apiece on eBay.

    I bought five spare batteries and charged them all in the router.

    John Hasson » Final&hellip  |  July 9th, 2008 at 2:46 pm

    [...] yet… off to do some research…)  Turns out the router lasts about 2 hours but there are tricks (not very sophisticated) to extend it.  The iPod Touch’s wifi usage battery life is only 3 hours anyways.  So… [...]

    Cradlepoint PHS300 Mini-R&hellip  |  January 7th, 2009 at 4:18 pm

    [...] phone battery (part number TXBAT10073) that are available cheaply on eBay.  Alternatively, you can create your own expanded battery pack out of five rechargeable [...]

    Philip Campbell  |  February 1st, 2009 at 10:08 am

    Hey there, i just got the phs300 and this battery hack sounds amazing – you should build them! – i would buy one. :)

    Jerry Billmyer  |  February 7th, 2009 at 9:12 pm

    I too have just gotten a PHS300. While battery life is not now a concern, the 3G store pointed out that if the ‘external battery’ voltage fall below 4.7V the unit looses its config and goes to mfg default. Solution, keep batteries charged or refreshed.

    I do have a problem, my 595U is not ‘seen’ by the PHS300, you mentioned a similar issue with yours. It involved connecting and reconnecting the modem? Was it software/firmware related in the router? The aircard works great on direct attachment to a PC/laptop. Thanks

    James Sammons  |  August 12th, 2009 at 3:31 am

    Maybe diodes would help as a safety measure for reversed polarity batteries. Just a thought…..I could be wrong about that.. lol

    Cradlepoint is my backup plan…I have a Verizon Expresscard and I’m considering the new MiFi Hotspot they are offering if they don’t try to make me change from my unlimited plan to a 5Gb/month plan. They told me I would have to for the device to work but I have a friend who works there that told me it was a ploy to get rid of the remaining unlimited plans. We shall see. Keep up the good work!

    novita  |  April 14th, 2010 at 1:20 pm

    i’m using phs-300S (sprint) , and trying to connect 885 att mercury as the usb modem (which is supported accrding to the list on website). But seem like th efirmware for phs300s and phs300 is different and it says inter connection is ready but connected
    and the modem led is RED.
    tried to flash with generic firmware but seems imcompatible… (i’ve tried to change some of the firmware header to match the sprint firmware but no luck …)
    any sugesstion…?

    Technojerry  |  May 1st, 2010 at 9:59 am

    I had to run a utility on a PC to make the AT&T Mercury not look like a USB storage device to the PHS300. I don’t have the S model, but the interal code in the Mecurcy kept the PHS300 from thinking it was a modem since it had been configured by the 3G Watcher app on my Mac. I got the link to the .exe from Cradleponit tech support.

    Jerry  |  May 1st, 2010 at 10:29 am

    Check this article for AT&T Mecury solutions for the PHS300.

    JoelAck  |  November 4th, 2010 at 3:42 pm

    I have the Sprint PHS300-S model and the Mercury AT&T modem. Cradelpoint support says there is no way to make them work. I think the Sprint model must have been subsidised by the carrier and they want to be sure you don’t use a competing carrier’s modem. The hardware (version 2) looks pretty generic, but you can’t reflash the firmware. Anybody who has solved this problem please let me know. Thanks in advance.

    Doogie  |  December 10th, 2010 at 10:59 pm

    To add to the battery packs, you need to be ware that the internal battery is only a 3.7v battery rated at 1800mah. if you were to “piggy back” off of the internal battery to allow the charger for the phs300 to charge them also you would only use 3 rechargeable “AA” batteries. if you were to use 4, it might cause a problem. Ideally you can use 6 AA rechargeable batteries in groups of 3 which should give 12+ hours of operation with the ability to still use the original charger to charge both the internal battery and the additional batteries at the same time. I used an enclosed holder and Velcro strips to attach them to the bottom of my cradlepoint. also used 2 9v battery connectors giving me a “disconnect” if I wanted to remove the packs!

    Dave  |  February 6th, 2011 at 3:47 pm

    Couple of points to add:

    Be sure to set transmitter power on the PHS-300 to minimum (settings available via

    Also, remember that you can disable LEDs of most modems (on Sprint modems, the setting is available if you use Sprint Smartview software, Prefs, Hardware, then select your modem, and click on ‘Edit Device Settings’. The disable LED check box is found there).

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