Mathias, head up to Radio Shack and get some roach clip wires that have them on both ends. They sell them like 5 or 6 in a pack already hooked up to wire for hooking things up like this. Then head to an auto parts store and buy a tail light bulb for a car or truck. Any will do so long as it's a regular bulb and not the newer helon or LCD ones and such. You want an old fashioned bulb that will suck down juice fast. They should all be 12V, like for a Ford Ranger or pretty much any car/truck that I know of. Look at the bulb's leads. Try to find out that only is used for the brake light and not other purposes so it only has two wires at the bottom of the connector for easy use. Doesn't matter if it has 2 on both sides. Just make sure you got one roach clip hooked to any on the left side of the base and one roach clip hooked to any on the right side of the base. If it all lights up (meaning if it has more than one filament in the bulb) then you've got it hooked up right. Just be aware that you aren't dead shorting the battery in some way with the leads and such in some way.
Let it sit on that bulb until it goes out and then another 30 minutes or so to insure all cells are equally flat. Some can get out of balance and the light might go out but some still have a charge, so let it sit. That's one way a pack gives poor run time because you put it on a charger and the charger thinks the pack is charged when a few cells reach full while others are still way low because of the inbalance. After you do this re-charge it for 10 hours (if the wall transformer says 100ma? then 10 hours for a 1000ma pack). Actually a full charge usually takes more time so I'd go another 2 hours or so maybe. Then drain it on the bulb again and re-charge. Do this cycle 4 or 5 times and see if it increases the run time. You need to excercise that pack. I know for sure it will fix it if you can blast charge it at 1 amp a few times on an aftermarket charge as this will break down crystals in the cells that the slow charge rate won't, but you still need to cycle it on the bulb 4 or 5 times when doing that too.