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I have a plain old mobile DVD player (Apex model PDVD-937). It runs on a single rechargeable battery supplying 1600mAh at 7.4V. I would like to augment it so that it can work for a longer period of time.

I've recently purchased an additional battery that is compatible with the original, albeit supplying only 1000mAh. I would like to wire the two batteries together so that I can enjoy a larger charge (2600mAh?) and longer time for playing DVDs on the device.

Being a complete electronics newbie I am guessing I need to hook the batteries in a series, but I've run into a problem. Each of the two batteries have three wires coming out of it: Red, Black and Yellow/White. Here's what it looks like:

Assuming Black for negative and Red for positive, what is the Yellow/White wire for? How should I setup the two batteries to get the longer operating duration for the device?

Olin Lathrop
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urig
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    The yellow/white wire could be a temperature sensor as Steve suugested. Some "smart" batteries contain a integrated charge controller and have extra wires for the system to talk to it. It looks like the model is readable, so maybe you can get hold of the datasheet. – Olin Lathrop Nov 21 '11 at 21:06

2 Answers2

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Series batteries is not what you want to do. If you connect them in series you will double your voltage and the DVD player probably wont be able to handle double the voltage. What you need to do to increase your life in this case is to put the batteries in parallel. This question explains a bit more about series/parallel.

The problem with this is that the batteries will drain at different rates, especially since they are rated for different mAh. When this happens you will end up having 1 battery charging the other battery, which is not exactly ideal.

To answer your specific question about what the 3rd wire is for, most likely this wire is a center tap between the 2 cells in the battery. This is used to be able to charge each cell independently of each other. If you don't have this connected, or connect the two batteries together, you will most likely cause the charging circuity in the DVD player to do some bad things.

My overall recommendation would be to just buy a single new batter with a greater mAh.

Community
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Kellenjb
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Connecting the batteries in series will add the voltage of the two and probably ruin your DVD player. The yellow white wire is likely from a temperature sensor which monitors the battery temperature during charging. If the battery were allowed to get to hot, it could start a fire or destroy the battery. To increase the battery current, the batteries would need to be wired in parallel, NOT series. However I DO NOT recommend doing this! First you have two different batteries, they will not share the load properly nor will they charge at the same rate. The charging circuit is designed for one battery @ 1.6AH and will react very different if the two batteries were connected in parallel. This could be dangerous, and will never work as you expect it to.

SteveR
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    It may indeed be a temperature sensor. I had originally written that in a comment, but decided to write a full answer instead an left that part out. However, it still also could be a center tap, but it would be hard to know with out testing it of finding a datasheet on it. – Kellenjb Nov 21 '11 at 20:30