OK> good to know it is 5 cells. This is a different issue. First - it will not hurt the receiver or most servos. Many people, myslef included, use 5-cell receiver packs. The servos will be faster and have more power. There is very little downside to using 5-cell instead of 4-cell.

However, charging is another matter. The wall wart charger that is rated at 50 mA (most likely) may only charge the pack at 20 or 30 mA or maybe not at all. And the light may go out long before the pack is charged. The wall charger is designed to charge a 4-cell pack at 50 mA. I have tested a few chargers with 5-cell packs and they tend to charge the pack at a lower rate. So if the charger is rated at 50 mA, it may be reduced to 30 mA with the 5-cell pack. So a 1100 mA pack may take 40 hours to charge.

If you have an ammeter, you can measure the charge rate. IF not, I'd find somebody to either measure the charge rate, or find someone that has a battery tester. Charge the pack with your charger and then have them discharge the pack and measure its capacity. Do this a couple times before you trust the wall charger.