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How To Rebuild A Sharp Mobilon Battery

striker Page Icon Posted 2006-03-01 12:40 PM
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I recently rebuilt my Sharp Mobilon HC-4500 battery. I did it in about 30 minutes, and it was very easy. The OEM rechargeable battery in the Mobilon is a 2.4v 2450mAh NiMH. When I got done, I had a 2.5v 2600NiMH. It works great!

NOTE: I am not responsible for any damage that happens if you attempt this. My rebuilt battery has been working better than new for 2 months now, so this information is only a synopsis of what I did.

Here's what I used:
- Xacto or similar thin blade knife
- Long, thin screwdriver
- Double-sided foam tape
- Super glue (optional)
- Replacement batteries (I used 2 AA 2600mAh NiMH cells - got a pack of 4 at Microcenter for $6. You can use any AA size NiMH rechargeable batteries, but the higher the "mAh" rating, the longer they'll last between charges. You'll need at least 2450mAh to match the stock battery pack. Do NOT use NiCad or any other rechargeable types - only Nickel Metal Hydride.)


Here's how to do it:

1. Remove the battery pack from the device.

2. Using an Xacto knife, cut along the bottom of the battery pack where the plastic comes together (see picture). You're cutting through the plastic, so don't be too gentle.

3. Get a thin screwdriver & pry the two plastic parts apart (top half & bottom half). Look at the polarity of the batteries inside - they follow the same polarity as normal batteries (flat side is -, the bump is +. Memorize what polarity goes to which side, so you don't put the new cells in backwards.

4. Remove the old batteries inside, using your screwdriver. You'll have two batteries, connected by a thermal fuse.

5. The batteries you removed are a little thicker than the AA cells you're putting in there. That's where the double sided foam tape comes in. I used the foam tape on the bottom of the battery holder & on the top, to hold the batteries in place. Cut thin strips of the foam tape & put it in now. Test fit everything by only removing one side of the tape, then put the batteries in & close the lid. The batteries might be a tight fit between the battery clips at the end, but they'll fit.

6. If everything fits, remove the other side of the tape & stick your new batteries in. I chose not to use the thermal fuse in my new setup, and it's been working fine for a couple months. If you choose to use it, you'll have to solder it in place yourself.

7. Put the top of the battery pack on. When you added foam tape, you should have added it to both sides of the plastic battery case, so when you stick everything together, the foam tape should hold everything together. If you have super glue, you can lay a bead down at the edges of the plastic, to glue the case back together. I didn't & mine works fine, but there's no harm in a little super glue (make sure you clamp the pack together if you glue).

8. Stick your new battery pack in your HPC. Plug the charger into the handheld & into the wall. If you did everything right, the "charging" light on the handheld should come on & your device should power on when you're done charging.
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David G Page Icon Posted 2006-03-01 1:41 PM
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Thanks Striker,

I've opened up my Mobilons dead battery pack.

The OEM batteries are tabbed and soldered together with the thermal fuse between the 2 batteries.

Are tabs present on your new batteries?

How did you fit the connections at the ends? (solder / springs / other neat ways of fitting?).
My high tech battery picture!
...................... _________ ... __________
Connnection ~[|_________|I[|__________|~ Connection
................... + (pos)....... Insulator/fuse...... - (neg)

Thanks
DG
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striker Page Icon Posted 2006-03-01 10:08 PM
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First of all, I used pliers to tear the tabs off the old batteries (while still keeping them attached to the connectors on the ). I cut two pieces of very thin (think under 0.5mm) scrap steel & used a dab of solder to attach them to the old battery connectors (the ones you just tore off the old batteries, but left attached to the connectors). Then I wedged the batteries in between my new makeshift battery contacts. Normal NiMH cells look exactly like Alkaline batteries, so there are no tabs on them - you just have to stick them in there.
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David G Page Icon Posted 2006-03-01 10:16 PM
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Sounds like a plan!

I'll tackle this one pretty soon.

Got to get me some batteries....


Thanks

DG
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cmonex Page Icon Posted 2006-03-02 3:27 PM
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thanks for posting this i may need it once..

thermal fuse: what is this for? sorry for the silly question, i'm very inexperienced in this.
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striker Page Icon Posted 2006-03-02 5:23 PM
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I believe it's used to prevent damage to the HPC if the batteries get too hot. It's just a safety thing - up to you whether or not to include it. I'd imagine normal AA batteries don't get as hot as the old cells in the stock battery pack, so I left mine out & it's been working fine so far.
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David G Page Icon Posted 2006-03-04 9:13 PM
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I refurbed my first battery pack today. I had already ordered some tabbed NiMH AA batteries from Thomas Distributing (Thomas Batteries - Ordered Tuesday - received Saturday via mail.).

They are 2000 mAh. I gave them a shot (even though they were less than the 2450 mAh the originals were rated at.) I soldered them in and used the double back tape method to hold the shell together.

I've charged them (and discharged them). So far they have behaved pretty good. I am testing them with my Belkin wireless card, and they've lasted longer than my other "good" battery.

I'll run them through a couple of good charge / discharge cycles and post the results.

DG
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David G Page Icon Posted 2006-03-06 11:52 AM
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Some battery benchmark results:

I used a freeware battery tracker software to track the of battery life time. This was not a perfect test as the unit would go into the auto screen dim mode and I would have to notice it and hit a key to wake it up. (The screen was set to about medium bright).

I kept the unit from going completely off during the entire test by having it Activesyn'ed to my PC.

With wireless card running (and activesync'ed through it): 1 hr. 8 min.
With no cards running and activesyncing through the serial cable 3 hr. 15 min.

My best battery life on my old cells before the rebuild was between 30 and 45 min.

I would judge my refurb to be a success.

Thanks for your help...

David Grissom
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nandoco Page Icon Posted 2006-03-16 10:20 AM
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Hey! So, I'm thinking about rebuilding my battery pack with 3600mah batteries. I'm just affraid it may damage the Mobilon due to long recharging period. So, what you think?

If you say it's too risky, I'm gonna use 2600 batteries instead.

tks.
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cmonex Page Icon Posted 2006-03-16 11:26 AM
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where can you find 3600 mAh AA sized batts??
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David G Page Icon Posted 2006-03-16 1:54 PM
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3600 mAh !

Where can you get them?

A side note: On my first charge cycle (fully discharged new battery) the battery pack heated up like crazy. Subsequent recharges were OK.

My thoughts - If you survive the first charge...you may be OK...

You may want to consider pre-charging the batteries before first use.

DG
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nandoco Page Icon Posted 2006-03-16 10:00 PM
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Guys, here in Brazil, our eBay (www.mercadolivre.com.br) has them available for R$ 35 ( 10 dolars ) . I don't know if they are real 3600 mah, since you should have them in the USA wayyy before than us. Anyway, here is the link for some of the offers (i know the links are strange, but they work)

http://produto.mercadolivre.com.br/MLB-41125011-4pilhas-recarregave...

http://produto.mercadolivre.com.br/MLB-41110634-4-pilhas-recarregav...

i'll test and let you know.

cmonex, who's the guy that also wants to build a ce software website?

tks
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Britty
Britty Page Icon Posted 2006-03-17 7:21 PM
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cmonex - 2006-03-03 6:27 AM

thanks for posting this i may need it once..

thermal fuse: what is this for? sorry for the silly question, i'm very inexperienced in this.


Thermal fuse protects the battery pack from overheating while charging. If the contents of the pack go over a predefined temp while charging (determined by the trip temperature of the fuse itself) the fuse will trip and cut the charge power to the batteries. This could happen if you are charging the batteries from absolute flat condition, in a very warm ambient temp. Once the contents cool down sufficiently the thermal fuse will reset and charging continues if it a self resetting type. If it is a once only type, it will need replacing once it trips.

However, like any fuse, it's main function is to protect the entire unit if any of the batteries go faulty/leaky and start dissipating more power than they normally would from the charger.

Faulty rechargables get pretty hot pretty quickly when they are being charged. Over time they eventually breakdown once this condition has started and the problem only gets worse the longer it is left unattended.

I would consider it unwise for anyone doing a refurbish on their battery pack to remove the thermal fuse altogether. One day you might need its services....

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cmonex Page Icon Posted 2006-03-17 8:32 PM
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nandoco - 2006-03-17 4:00 AM

Guys, here in Brazil, our eBay (www.mercadolivre.com.br) has them available for R$ 35 ( 10 dolars ) . I don't know if they are real 3600 mah, since you should have them in the USA wayyy before than us. Anyway, here is the link for some of the offers (i know the links are strange, but they work)

http://produto.mercadolivre.com.br/MLB-41125011-4pilhas-recarregave...

http://produto.mercadolivre.com.br/MLB-41110634-4-pilhas-recarregav...

i'll test and let you know.

cmonex, who's the guy that also wants to build a ce software website?

tks


wow this is real 3600 mAh..

he's mscdex
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nandoco Page Icon Posted 2006-03-18 12:00 PM
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SHIT! I lost my thermal fuse, could anyone give me info on this piece of hardware cause I wann buy one to build the 3600 mah battery pack.

tks.
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