I've been told that I probably have a bad cell in my battery pack, a 7 cell, 700 mAmp, 8.4 Volt Ni-Mh. It won't take a full charge. How do I find out? I assume I will have to de-solder the pack, but how will I check each of the cells properly? I'm electron challenged.
Steve

Take the heat shrink off of the pack. Use a volt meter to check each cell for voltage. You don't have to desolder to check the cells. The good cells will have about the same voltage. The bad cells will be obvious.

Roger that! You can also just jab the probe through the heat shrink, just make sure you have the polarity right.

Jetts

Unless you're real good with soldering I wouldn't bother trying to determine the bad cell, just replace the whole pack. Even if you replace the bad one, there's a good chance that another of those cells will go bad soon.
Dennis-

Yes, unless it's a Hitec "Focus 4"Tx, then you can just slide a new one in the "pack".
Been O.K. for two years now.

Jetts

If one cell is bad, the others are probably not far behind.

I'ld just replace the pack. If you replace one cell it will be different from the others and not charge well.

I had JR radio with Sanyo batts. Had an RX cell fail. Replaced pack. 2 moths later the TX pack failed. Must have been a bad lot. Replaced both and they worked for 10 years. Still test at 100% of capacity.

I also say don't replace just one cell in a battery pack.

The other old cells were probably form the same manufacturer's lot as the one that failed. and they have had the same amount of use. They will be very likely to fail soon. May as well replace them all.

Why trust your model to a debateable condition battery?

Hmm... try to save $20 to $30... and risk $300 to $3000 worth of airplane. Does that sound like a good plan?

You can go to Wal-Mart, get 8 AA NiMH cells (1800 mah) for appx $18... and solder up a TX pack if you want to play with soldering on a battery. (it works well... but you HAVE to know what you are doing to get good joints!) I am right now operating my TX and RX on battery packs made this way... but I have a friend who is VERY good at soldering up battery packs and does a professional quality job of it. (I don't trust my solder joints on batteries.... and I do pretty well at soldering... Think about it.)

If this is a 7 cell pack, I would assume that it not a receiver pack, but a Motor pack. If this is correct, don't worry about replacing one cell. If another goes bad, you're not going to lose your plane.

To summerize: If this is just a pack for an electric motor, I would replace just the one cell.

FHHuber - What brand name battery are you buying at Wal-Mart? Sounds like a very good price for NiMH's.

Roger that.
As I was tryin' to say, not everyone-especially newbies, have the bucks to "just buy" a new pack or whatever. It's good to be a little thrifty, and learn/know how to change things.
Not insinuating anyone "risk 300-3000 bucks to save 20-30." How rediculous is that?

Jetts

Hi guys, I appreciate the the help you have given. The 7 cell is in fact a motor battery. I use it in my Slow Stick. The pack is not very old and I do have good soldering skills. I thought that if I inserted voltmeter probes on each end of a cell that was soldered together in a pack, the reading would be an indication of the entire pack rather than the individual cell. It seems that if I want to check the cells individually, then they should not be wired in a pack. Thanks
Steve

By the way, the cells at Walmart, AA 1800 mAmp must be the Energizer rechargeables. I don't think that they can stand up to a fast charge like we prefer to use on everything.

You are corret which cells they are. No, I don't fast charge them. (who needs to?... you can get 4 hours flight time without recharge.) And I do have a charger that peak detects for NiMh....

There are some 2100 mah fast chargeable NiMh's available at Wal-Mart... I may be looking at my next repacement batteries. I will have to get some and test a bit for reliability before trusting a model to them.... (I never blindly trust new tech.)

Steve,
You can just stick the probe through the plastic, and get the ends of the battery, it will tell the voltage of that cell, even if they are soldered. Remember to switch sides with the probes for each cell in sequence, or you'll get a neg. voltage reading on every other one. (Still will give an indication of a bad cell).

Jetts