Just wondered if anyone knew of any classic boomboxes from the 80s or 90s that people have moded with an internal rechargeable battery?  I thought I read a post somewhere of one guy building a battery from a number of mobile phone lithium batteries which gave him over 30 hours battery life.

I would love to attempt a mod like this myself, but would love to see examples of models that people have already moded to help me in selecting a suitable unit.

Thanks Tony

I'm not an expert, nor have I done this yet, but am planning to soon. One option is to buy rechargeable D cells. You can get an 8-pack of the best brand Ni-Mh for $60 on ebay or amazon, and theoretically they should give much better run-time than Alkalines. I thought about this but then adding a charger sends the price pretty high.

Another option is to build a battery pack from the cells used for RC cars. This is slightly more cost effective if you buy them right. Check places like Hobby King or all-batteries.

I have no experience with the big pack of li-ion cell-phone batteries but I'd encourage you to look elsewhere as charging such a setup would likely be tedious, dangerous, or both.

Good luck!

Every time I open up a box I build a charge plug into it. So I can leave the rechargeable d cells in it to have them charged inside the box. It's standard procedure for every box by now 

I'm using a plug with a switch that cuts of the batts from the radio circuit while charging. I'm using a rc charger that starts speed charging with 3 amps and goes down to 200 mAmp idle. Using cheap Lidl d cells  Works great and it's very convenient, making the machine a real portable 

Michiel, that sounds pretty awesome! Can you please provide further details, instructions, or parts lists for your charging circuit?

Do you plug in AC or DC to the box?

Is the switch automatic, so that when power is applied the batteries are automatically taken out of the circuit, or do you flip a physical switch?

Also, what is Lidl? Is that a LSD NiMh similar to Eneloop?

Its all very basic and cheap. It takes 5 or 10 min to build it into the box. Here are some pics of it and a simple schematic.

The complete set:

DC plug, male and female. Center pin is negative.

D cells. Lidl is a supermarket that sells them sometimes. They are around 4 euros for two of them.

How its all connected. When you plug in the charger cord, the plus to the radio circuit is disconected. Pin number 3 of the DC plug gets disconnected of pin 2.

Thats all!

cheers Michiel

Oh, very cool! Thanks for the info. This is a great way to go as it requires little modding of the box and is super cost effective. How would you estimate the runtime compares to Alkaline D cells? I see you've got 4500mAh cells. For more money you can get up to 11000mAh cells for really long runtime!

I would even consider integrating a charger into the box if you could source a small & cheap enough unit. That way, all you need is an AC cable and you're all set. 

In the Hitachi the batts last about 10 to 12 hours. Every time the box gets some rest, I stick it to the charger cable for idle charge. So it's hardly ever empty. Fast charging takes less than 2 hours, but I charge them well beyond the advised current. Till now they are still working okay.

With higher capacity batts you also need a stronger (and heavier) charger. Or need more time to charge. Higher cap batts would be better if you do it the normal way, like with charging the batts outside the box.

Building an integrated charger would be nice, but it ads weight to the box and gets expensive if you've got lots of boxes. Also don't think the original power supply of the box has enough capacity. But it would be a nice project.. Small circuits for safely charging nimh bats do exist. 

I tested the batt performance the last couple of days. The Hitachi played for about 30 hours on a single charge.  Volume around 3 to 4 (pretty loud on this box) and using the iPod on line-in. Not bad! 

Hey Michiel - I've just bought a Clairtone 7890 and I'm pumped to get a modification like the one you've outlined.

I am still learning about batteries, but from my old RC days - I know that there are some cool custom chargers out there.

Would you mind taking a look to see if something like this could work:

• 10 NiMH D cell batteries 10,000mah
• An all purpose charger like this: http://www.batteryspace.com/Mu...d-Battery-Pack.aspx#
• • I noticed that the second thumbnail shows a 2.5mm barrel connector (like yours?).

If the above did work, I'd love to find a way to mount the charger itself on the unit so all I needed was an AC cord.  

Doable you think?

Looking good! I still apply the method and it works great. I don't know if the charger you linked is able to charge those high mah cells in a reasonable time tho. It looks a bit small and not really powerful. They don't mention any charging specs, do they? I'm pushing about 3amps in to my cells that are half as powerful. 

I got the plug and jacks from an electronics store. I think it's about 6mm. I would expect a RC store has the same plugs for sale. I replaced the tamiya plug.

I never tried to build a charger inside a box. But if there is enough space, it should not be a problem. You could try to use the switch in ac plug to disconnect the batts from the radio circuit while charging.