The problem isn't the battery, it's the stock wall charger you're using. The wall charger is probably not charging the batteries properly.
Do yourself a favour - spend some money on a proper charger. A good smart charger will run about $80 and will balance charge your batteries. If you can't afford that, spend $35 on a cheap balance charger that is suitable for NiCad & NiMH batteries.
With a smart charger, charge your batteries at the voltage rating of your battery pack, and 10-20% of its mAh rating. E.g., for a 9.6 V 1600 mAh battery on a smart charger, setup the charger for 9.6 V, and 160 mAh charge rate. This will tell the charger to fill the battery at a rate of 160 mAh at 9.6 V, which will take about 10 hours. (Note that most smart chargers can be set in 1/10 of an amp, so settings will be more likely 100 mAh, 200 mAh, etc. I set for 200 mAh, and it takes about 8 hrs to charge.) This will fill your battery to about 95% capacity (9.5 hrs continuous usage, in theory) which is more than enough for a day's game. You can also charge at higher than 10-20% of mAh, but not higher than 50% of mAh. However, the lower mAh/longer charge time provides better battery performance and longevity in the field.
The cheap balance chargers are just plug-and-play, and lets you know when a battery is fully charged with a green indicator light. Charge times are usually about 4-5 hrs. They're fairly good at charging batteries without setup or fuss.
Continued use of the wall (dumb) charger will only kill your batteries.
VFC SCAR-L - VFC SCAR SSR - KJW Hi-Capa 5.1 - CAW M79
The Three Sisters - WE G39 E/K/C
Originally Posted by kalnaren
Stalker stays where he is.
His BB's fly across the country to hit their target.